Docs: Initial documentation structure using Sphinx (#5355)

This PR is the initial documentation structure including the basic information about the project and Sphinx configuration.

####CONTENTS:
- Getting Started
- Installing
- Boards
- Libraries
- Library Builder
- Tutorials
- ESP-IDF as Component
- OTA Web Update
- makeEspArduino
- Troubleshooting
- Contributing

This PR also changes the README.md.

docs/source/boards/generic.rst

@@ -0,0 +1,34 @@
+####################
+Generic ESP32 Boards
+####################
+
+Specifications
+--------------
+
+Add here the board/kit specifications.
+
+Header Block
+------------
+
+Header1
+^^^^^^^
+===  ====  =====  ===================================
+No.  Name  Type   Function
+===  ====  =====  ===================================
+1    3V3   P      3.3 V power supply
+2    IO0   I/O    GPIO0, Boot
+3    5V0   P      5 V power supply
+4    GND   G      Ground
+===  ====  =====  ===================================
+
+Pin Layout
+----------
+
+Add here the pin layout image (not required).
+
+Resources
+---------
+
+* `ESP32`_ (Datasheet)
+
+.. _ESP32: https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf