[Docs] Added I2C driver docs (#5770)

* Added I2C driver docs
docs: Changes on the images and added more details about the I2C slave

* docs: Added slaveWrite description and added docs build folder to the gitignore file

.gitignore

@@ -21,3 +21,4 @@ boards.sloeber.txt
 
 # Ignore docs build (Sphinx)
 docs/build
+docs/source/_build

docs/source/libraries.rst

@@ -2,7 +2,7 @@
 Libraries
 #########
 
-Here is where the Libraries API's descriptions are located.
+Here is where the Libraries API's descriptions are located:
 
 Supported Peripherals
 ---------------------
@@ -63,6 +63,7 @@ The Arduino ESP32 offers some unique APIs, described in this section:
     Deep Sleep <api/deepsleep>
     ESPNOW <api/espnow>
     GPIO <api/gpio>
+    I2C <api/i2c>
     RainMaker <api/rainmaker>
     Reset Reason <api/reset_reason>
     Wi-Fi <api/wifi>