Add liberapay, change pr template

.gitea/PULL_REQUEST_TEMPLATE.md

-[ ] I agree to release my code and all other changes of this PR under the AGPL-3.0 license
+- [ ] I agree to release my code and all other changes of this PR under the AGPL-3.0 license

README.md

 # Matrix Homeserver in Rust
 
+![Liberapay](http://img.shields.io/liberapay/receives/timokoesters.svg?logo=liberapay)
+
 #### Goals
 
 A Matrix Homeserver that's faster than others.
@@ -24,3 +26,7 @@ #### Roadmap
 - [ ] Riot E2EE
 - [ ] Basic federation
 - [ ] State resolution
+
+#### Donate
+
+Liberapay: <https://liberapay.com/timokoesters/>