[docs] Restructure documentation, clarify some parts

docs/getting-started/README.md

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+# Getting started
+
+Using LibreTuya is simple, just like every other PlatformIO development platform.
+
+1. [Install PlatformIO](https://platformio.org/platformio-ide)
+2. `platformio platform install https://github.com/kuba2k2/libretuya`
+
+## Board selection
+
+- Go to [Boards & CPU list](../status/supported.md).
+- Find the board your device has (usually, the model number is written on the silkscreen).
+	- If your board isn't available yet, use one of the "Generic" boards that matches the CPU you have.
+- Click on the board name. From the documentation page, note the board code.
+- Use this code to create a PlatformIO project.
+
+## GPIO usage
+
+!!! important
+	This can be confusing at first, so make sure to read this part carefully to understand it.
+
+	Input/output pin numbers in Arduino code (i.e. `digitalWrite()`) use Arduino pin numbers - for example `D1`, `D3`. This is the same as simply `1` or `3`, but it cannot be confused with CPU GPIO numbers.
+
+	On the board pinout page, the purple blocks represent Arduino pins, while the dark red blocks refer to GPIO numbers.
+
+	Projects like ESPHome also use Arduino pin numbering.
+
+## Develop your own project
+
+If you're developing your own embedded software, and want it to run on LibreTuya-supported chips, create a project.
+
+- use PlatformIO IDE (PIO Home -> Open -> New Project)
+- run `pio project init` in your desired project directory
+
+Next, read [Uploading](uploading.md) guide to run your project!
+
+## Run community projects
+
+LibreTuya was developed with popular community projects in mind. Currently, unofficial [ESPHome port](../projects/esphome.md) is available ([the PR](https://github.com/esphome/esphome/pull/3509) will hopefully be merged into upstream at some point).