Update README

Author: rleh

README.md

@@ -1,7 +1,5 @@
 # Up-to-date AVR GNU GCC Toolchain from source
 
-[![CircleCI](https://circleci.com/gh/modm-ext/docker-avr-gcc.svg?style=svg)](https://circleci.com/gh/modm-ext/docker-avr-gcc)
-
 ## Installation
 
 Download the latest `avr-gcc.tar.bz2` from [Releases](https://github.com/modm-ext/docker-avr-gcc/releases)
@@ -49,9 +47,9 @@ time ./build.sh
 
 The toolchain will be in `/opt/avr-gcc`.
 
-## Building in CircleCI
+## Building in Github Actions
 
-There is a CircleCI job defined in `.circleci/config.yml` which builds the
-toolchain using the Docker container. For tagged commits, a Github release
-will be created with the toolchain put into a downloadable `.tar.bz2` at
+There is a Github Actions job defined in `.github/workflows/` which builds the
+toolchain. For tagged commits, a Github release will be created with the
+toolchain put into a downloadable `.tar.bz2` at
 [Releases](https://github.com/modm-ext/docker-avr-gcc/releases).