spell fixes

Author: ZodiusInfuser

REFERENCE.md

@@ -143,7 +143,7 @@ The expected value is either `0` or `1`, or `True` or `False`.
 
 ### As Encoder
 
-In addition to the input and output functions of GPIO pins, they can also be paired together to read rotary encoders like those used on dials or for motor feedback. Up to two encoders are supported in this way. This is in addtion to the two encoders already in use by the motor connectors.
+In addition to the input and output functions of GPIO pins, they can also be paired together to read rotary encoders like those used on dials or for motor feedback. Up to two encoders are supported in this way. This is in addition to the two encoders already in use by the motor connectors.
 
 To start using GPIO pins for an encoder, first import their handy constants:
 

docs/plasma.md

@@ -12,11 +12,11 @@ Under the hood Plasma uses the [rpi_ws281x package](https://pypi.org/project/rpi
 - [Clear all LEDs](#clear-all-leds)
 - [Delayed Showing](#delayed-showing)
 - [Function Reference](#function-reference)
-- [DummyPlasma](#dummyplasma)
+  - [DummyPlasma](#dummyplasma)
 
 ## Getting Started
 
-`InventorHATMini` automatically creates a `Plasma` instance, accessable by `board.leds`. Instructions for creating a standalone instance are provided below for completeness.
+`InventorHATMini` automatically creates a `Plasma` instance, accessible by `board.leds`. Instructions for creating a standalone instance are provided below for completeness.
 
 To construct a new `Plasma` instance, specify the number of LEDs, and the GPIO pin to use. See [GPIO Usage](https://github.com/rpi-ws281x/rpi-ws281x-python/tree/master/library#gpio-usage) for details on what pins are supported.