Update contributing guidelines

CONTRIBUTING.md

@@ -1,13 +1,15 @@
 # Contributing
 
-No preference. If you know how to use Github and have contributed to open source projects before then:
+This project is hosted on a self-hosted [Gitea](https://gitea.io/en-us/)
+instance. If you know how to use Github and have contributed to open source
+projects before then, you'll feel right at home. Github OAuth is also enabled
+so you can easily create an account and start contributing right away:
 
-* File an issue
-* Submit a pull request
-* File an issue + Submit a pull request
-* Use this project somewhere :)
+- File an issue
+- Submit a pull request
+- File an issue + Submit a pull request
+- Use this project somewhere :)
 
-Be sure to add yourself to the [AUTHORS](/AUTHORS)
-file when you submit your PR(s). Every contribution counts no how big or small!
+Be sure to add yourself to the [AUTHORS](./AUTHORS) file when you submit your PR(s). Every contribution counts no how big or small!
 
-Thanks for using twtxt!
+Thanks for using this project!