RGB Driver Documentation Update (#3601)

- Minor formating in rgb matrix page
- Added a short discription for is31fl3731 in drivers page

docs/feature_rgb_matrix.md

@@ -107,7 +107,7 @@ These are the effects that are currently available:
 Custom layer effects can be done by defining this in your `<keyboard>.c`:
 
     void rgb_matrix_indicators_kb(void) {
-    	// rgb_matrix_set_color(index, red, green, blue);
+        rgb_matrix_set_color(index, red, green, blue);
     }
 
 A similar function works in the keymap as `rgb_matrix_indicators_user`.

docs/hardware_drivers.md

@@ -25,3 +25,7 @@ You can make use of uGFX within QMK to drive character and graphic LCD's, LED ar
 ## WS2812 (AVR Only)
 
 Support for WS2811/WS2812{a,b,c} LED's. For more information see the [RGB Light](feature_rgblight.md) page.
+
+## IS31FL3731 (AVR Only)
+
+Support for up to 2 drivers. Each driver impliments 2 charlieplex matrices to individually address LEDs using I2C. This allows up to 144 same color LEDs or 32 RGB LEDs. For more information on how to setup the driver see the [RGB Matrix](feature_rgb_matrix.md) page.