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/lib_builder.rst

@@ -0,0 +1,38 @@
+###############
+Library Builder
+###############
+
+How to Use Library Builder
+--------------------------
+
+Espressif has provided a `tool <https://github.com/espressif/esp32-arduino-lib-builder>`_ to simplify building your own compiled libraries for use in Arduino IDE (or your favorite IDE).
+To generate custom libraries, follow these steps:
+
+
+- Step 1 - Clone the ESP32 Arduino lib builder::
+
+    git clone https://github.com/espressif/esp32-arduino-lib-builder
+
+- Step 2 - Go to the ``esp32-arduino-lib-builder`` folder::
+
+    cd esp32-arduino-lib-builder
+
+- Step 3 - Run the ``update-components`` script::
+
+    ./tools/update-components.sh`
+
+- Step 4 - Run ``install-esp-idf`` installation script (if you already have an ``$IDF_PATH`` defined, it will use your local copy of the repository)::
+
+    ./tools/install-esp-idf.sh
+
+- Step 5 - Copy the configuration (recommended) or directly edit sdkconfig using ``idf.py menuconfig``::
+
+    cp sdkconfig.esp32s2 sdkconfig
+
+- Step 6 - Build::
+
+    idf.py build
+
+The script automates the process of building `Arduino as an ESP-IDF component <https://github.com/espressif/arduino-esp32/blob/master/docs/esp-idf_component.md>`_.
+Once it is complete, you can cherry pick the needed libraries from ``out/tools/sdk/lib``, or run ``tools/copy-to-arduino.sh`` to copy the entire built system.
+``tools/config.sh`` contains a number of variables that control the process, particularly the ``$IDF_BRANCH`` variable.  You can adjust this to try building against newer versions, but there are absolutely no guarantees that any components will work or even successfully compile against a newer IDF.