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/esp-idf_component.rst

@@ -0,0 +1,92 @@
+##############################
+Arduino as a ESP-IDF component
+##############################
+
+ESP32 Arduino lib-builder
+-------------------------
+
+For a simplified method, see `lib-builder <lib_builder>`_.
+
+Installation
+------------
+
+- Download and install `ESP-IDF <https://github.com/espressif/esp-idf>`_.
+- Create blank idf project (from one of the examples).
+- In the project folder, create a new folder called `components` and clone this repository inside the new created folder.
+
+.. code-block:: bash
+    
+    mkdir -p components && \
+    cd components && \
+    git clone https://github.com/espressif/arduino-esp32.git arduino && \
+    cd arduino && \
+    git submodule update --init --recursive && \
+    cd ../.. && \
+    idf.py menuconfig
+
+
+- The `idf.py menuconfig` has some Arduino options.
+    - On `Autostart Arduino setup and loop on boot`.
+        - If you enable these options, your main.cpp should be formated like any other sketch.
+
+.. code-block:: c
+
+    //file: main.cpp
+    #include "Arduino.h"
+
+    void setup(){
+        Serial.begin(115200);
+    }
+
+    void loop(){
+        Serial.println("loop");
+        delay(1000);
+    }
+
+- Otherwise, you need to implement ```app_main()``` and call ```initArduino();``` in it.
+
+Keep in mind that setup() and loop() will not be called in this case.
+If you plan to base your code on examples provided in `examples <https://github.com/espressif/esp-idf/tree/master/examples>`_, please make sure to move the app_main() function in main.cpp from the files in the example.
+
+.. code-block:: cpp
+
+    //file: main.cpp
+    #include "Arduino.h"
+
+    extern "C" void app_main()
+    {
+        initArduino();
+        pinMode(4, OUTPUT);
+        digitalWrite(4, HIGH);
+        //do your own thing
+    }
+
+- "Disable mutex locks for HAL"
+- If enabled, there will be no protection on the drivers from concurently accessing them from another thread/interrupt/core
+    - "Autoconnect WiFi on boot"
+- If enabled, WiFi will start with the last known configuration
+- Otherwise it will wait for WiFi.begin
+
+- ```idf.py -p <your-board-serial-port> flash monitor``` will build, upload and open serial monitor to your board
+
+Logging To Serial
+-----------------
+
+If you are writing code that does not require Arduino to compile and you want your `ESP_LOGx` macros to work in Arduino IDE, you can enable the compatibility by adding the following lines after:
+
+.. code-block:: c
+
+    #ifdef ARDUINO_ARCH_ESP32
+    #include "esp32-hal-log.h"
+    #endif
+
+FreeRTOS Tick Rate (Hz)
+-----------------------
+
+You might notice that Arduino-esp32's `delay()` function will only work in multiples of 10ms. That is because, by default, esp-idf handles task events 100 times per second.
+To fix that behavior, you need to set FreeRTOS tick rate to 1000Hz in `make menuconfig` -> `Component config` -> `FreeRTOS` -> `Tick rate`.
+
+Compilation Errors
+------------------
+
+As commits are made to esp-idf and submodules, the codebases can develop incompatibilities which cause compilation errors.  If you have problems compiling, follow the instructions in `Issue #1142 <https://github.com/espressif/arduino-esp32/issues/1142>`_ to roll esp-idf back to a different version.