Documentation (#769)

* spelling correction

* Restuctured, added "features", "supported hardware", intro for developers and links to the developer documentation.

* Spelling correction

* URL correction

* Documentation restructure

* Moving developer documentation index from top level README to Documentation directory README

* fixing URLS

* Restructuring and adding to board config

* Improving navigation of docs oon github

* New line after first heading

(https://github.com/home-assistant/operating-system/pull/768#discussion_r453336692)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Update README.md

https://github.com/home-assistant/operating-system/pull/768#discussion_r453336871

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Update README.md

(https://github.com/home-assistant/operating-system/pull/768#discussion_r453336999)
- Surround headings with newlines
- ODROID
- Use dashes for unordered lists

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Update README.md

- new line after heading
(https://github.com/home-assistant/operating-system/pull/768#discussion_r453337043)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Update README.md

- \- for unordered lists
- new line after heading
(https://github.com/home-assistant/operating-system/pull/768#discussion_r453337101)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Update README.md

- new line after heading
- \- for unordered lists
(https://github.com/home-assistant/operating-system/pull/768#discussion_r453337183)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

* Spelling correction, to ensure /Dpcumentation/kernel.mdhas the correct spelling

* capitalisation

* using - for unordered lists

* Adding links to config files

* fixing links to _defconfig files

* fixing link for rpi0_w

* fixing link for rpi3_64 and rpi4_64

* making the ova README consistent with the others

* formmating

* fixing numbered list

* fixing indent for sub-bullets

* questions regarding Tinker S and OVA support

* resolving PR comment from fabaff

* resolving PR comment from fabaff

* https://github.com/home-assistant/operating-system/pull/769\#discussion_r456774209

* Changing uBoot to U-Boot (https://github.com/home-assistant/operating-system/pull/769#discussion_r456774290)

* s/boot sector/eMMC boot partition/ (See https://github.com/home-assistant/operating-system/pull/769#discussion_r456774329)

* As per comments here:
https://github.com/home-assistant/operating-system/pull/769#discussion_r456791491
https://github.com/home-assistant/operating-system/pull/769#discussion_r456791580

* HassOS is no longer the official name (https://github.com/home-assistant/operating-system/pull/769#discussion_r456791863)

* Should be Home Assistant Operating System (or OS) (see https://community.home-assistant.io/t/changing-the-home-assistant-brand/167500/16). See also commennts here https://github.com/home-assistant/operating-system/pull/769#discussion_r456793030, taken in to account along with previous comments about this paragraph.

* s/HassOS/Home Assistant Operating System/

* 8Gb Pi 4 will be supported soon (see comment https://github.com/home-assistant/operating-system/pull/769#discussion_r459768349)

* resolving conflict with main dev branch.

Co-authored-by: Franck Nijhof <frenck@frenck.nl>
Co-authored-by: Pascal Vizeli <pvizeli@syshack.ch>

Documentation/boards/README.md

@@ -0,0 +1,53 @@
+# Boards
+
+## Overview
+
+The following boards/devices are supported:
+
+- Raspberry Pi
+  - Pi 4 Model B (1 GB, 2 GB and 4 GB model) 32-bit (recommended)
+  - Pi 4 Model B (1 GB, 2 GB and 4 GB model) 64-bit
+  - Pi 3 Model B and B+ 32-bit (recommended)
+  - Pi 3 Model B and B+ 64-bit
+  - Pi 2 (not recommended)
+  - Pi Zero-W (not recommended)
+  - Pi (not recommended)
+- Hardkernel
+  - Odroid-C2
+  - Odroid-N2
+  - Odroid-XU4
+- Intel NUC
+  - Intel NUC5CPYH
+  - Intel NUC6CAYH
+  - Intel NUC10I3FNK2
+  - Gigabyte GB-BPCE-3455
+  - Others recent Intel NUC computers are likely to work too, only those listed above have been tested.
+- Asus
+  - Tinker Board
+- Virtual appliance (x86_64/UEFI):
+  - VMDK
+  - OVA ?
+  - VHDX ?
+  - VDI ?
+  - QCOW2 ?
+
+Notes:
+  - see ? above: are these currently supported? see ova documentation which explains issues with previous OVA distribution)
+
+## Board specifics
+
+|Board|Build|Config|Docs|
+|-----|----|------|----|
+|Pi4B 32-bit |`make rpi4`      |[rpi4](../../buildroot-external/configs/rpi4_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi4B 64-bit |`make rpi4_64`   |[rpi4_64](../../buildroot-external/configs/rpi4_64_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi3B 32-bit |`make rpi3`      |[rpi3](../../buildroot-external/configs/rpi3_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi3B 64-bit |`make rpi3_64`   |[rpi3_64](../../buildroot-external/configs/rpi3_64_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi2         |`make rpi2`      |[rpi2](../../buildroot-external/configs/rpi2_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi Zero     |`make rpi0_w`    |[rpi0_w](../../buildroot-external/configs/rpi0_w_defconfig)|[raspberrypi](./raspberrypi/)|
+|Pi          |`make rpi`       |[rpi](../../buildroot-external/configs/rpi_defconfig)|[raspberrypi](./raspberrypi/)|
+|Odroid-C2   |`make odroid_c2` |[odroid_c2](../../buildroot-external/configs/odroid_c2_defconfig)|[hardkernel](./hardkernel/)|
+|Odroid-N2   |`make odroid_n2` |[odroid_n2](../../buildroot-external/configs/odroid_n2_defconfig)|[hardkernel](./hardkernel/)|
+|Odroid-XU4  |`make odroid_xu4`|[odroid_xu4](../../buildroot-external/configs/odroid_xu4_defconfig)|[hardkernel](./hardkernel/)|
+|NUC         |`make intel_nuc` |[intel_nuc](../../buildroot-external/configs/intel_nuc_defconfig)|[intel](./intel/)|
+|Tinker Board|`make tinker`    |[tinker](../../buildroot-external/configs/tinker_defconfig)|[asus](./asus/)|
+|OVA         |`make ova`       |[ova](../../buildroot-external/configs/ova_defconfig)|[ova](./ova/)|