start writing Documentation

Signed-off-by: Dhruva Gole <[email protected]>

Author: DhruvaG2000

Documentation/overlays.md

@@ -0,0 +1,3 @@
+# DT Overlays
+
+TODO

Documentation/variants.md

@@ -0,0 +1,30 @@
+# How to add custom boards
+
+**Pre-reqs:** <br>
+- It is most recommended that if you have a highly custom board that even zephyr-RTOS doesn't support yet then you should add support for it first there.
+- You need to satisfy all requirements mentioned in the project's README.
+
+**General Instructions:** <br>
+- The project is structures in a way so as to isolate the variants from the core API. Thus, whenever a new board needs to be added it needs to be done in the `variants/` folder.
+- The structure of the variants folder with the help of an example is as follows:
+```tree
+variants/
+├── ARDUINO_NANO33BLE
+│   ├── arduino_nano_33_ble.overlay
+│   └── arduino_nano_ble_sense_pinmap.h
+├── CMakeLists.txt
+└── variants.h
+```
+
+- The top level consists of `CMakeLists.txt`, `variants.h` and the `<BOARD_NAME>` folder. Each of these files have a specific role to play.
+		- The `Cmakelists` help the compiler locate the proper directory to help find the proper header files that are board specific. You need to add the name using `zephyr_include_directories(BOARD_NAME)` to this file. Do note that this `BOARD_NAME` is the same as the name of your board's directory.
+		- `variants.h` contains the necessary `#includes` inorder to tell the source code about your board's pinmap.
+- The `<BOARD_NAME>` folder is where the overlay and pinmap file resides. Inorder to understand how to write DT overlays, lookup `Documentation/overlays.md`. To understand the `<boardname_pinmap.h> file, go through the existing `variants/ARDUINO_NANO33BLE/arduino_nano_ble_sense_pinmap.h` which shows how to use the overlay nodes inside our C programs using zephyr macros like `GPIO_DT_SPEC_GET`. The zephyr-project documentation on this is pretty extensive as well and worth reading.
+
+## Suppored Boards/variants
+
+- [X] Arduino Nano ble sense 33
+- [X] Arduino Nano ble 33
+
+## Planned Support: (TODO)
+- [ ] Particle Xenon