docs: fix typo and clarify extending

Author: Warrobot10

README.md

@@ -138,9 +138,9 @@ refer to the [Hardware Section of the API-Documentation](https://sensorium.githu
 External chips (DAC) can also be used on any platform which does not support natively the I2S protocol  using an user defined `audioOutput` function. This can allow a greater audio quality over the native ways to output the sound (PWM for AVR Arduinos and STM32 and 12 bit DAC for Teensy 3.*).
 Examples are provided for the MCP492X DAC (12 bit on SPI) and for the (PT8211) 16 bit stereo DAC using SPI port to emulate the I2S protocol. The latter should be compatible with any DAC using I2S.
 
-### Extendig the library itself
+### Extending the library itself
 
-If you enjoy using Mozzi for a project, or have extended it, we would be
+If you enjoy using Mozzi for a project, or have made changes or otherwise extended it, we would be
 pleased to hear about it and provide support wherever possible. Contribute
 suggestions, improvements and bug fixes to the Mozzi wiki on Github, or
 Fork it to contribute directly to future developments.