Added lib builder and esp-idf as component rst files

Author: pedrominatel

docs/source/esp-idf_component.rst

@@ -0,0 +1,2 @@
+ESP-IDF as Component
+====================

docs/source/index.rst

@@ -1,5 +1,5 @@
 Welcome to ESP32 Arduino Core's documentation
-================================================
+=============================================
 
 .. toctree::
    :maxdepth: 2
@@ -9,3 +9,5 @@ Welcome to ESP32 Arduino Core's documentation
    Installing <installing>
    Boards <boards/boards>
    Libraries <libraries>
+   Library Builder <lib_builder>
+   ESP-IDF as Component <esp-idf_component>

docs/source/lib_builder.rst

@@ -0,0 +1,24 @@
+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 use it to generate custom libraries, follow these steps:
+
+
+- Ubuntu and Debian::
+
+git clone https://github.com/espressif/esp32-arduino-lib-builder
+
+#. Step 1. ``
+#. Step 2. `cd esp32-arduino-lib-builder`
+#. Step 3. `./tools/update-components.sh`
+#. Step 4. `./tools/install-esp-idf.sh` (if you already have an $IDF_PATH defined, it will use your local copy of the repository)
+#. Step 5. `make menuconfig` or directly edit sdkconfig.
+#. Step 6. `./build.sh`
+
+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.