replace the azure link in the readme
the readme contained a url to the azure pipelines which were replaced with
GitHub actions in (c9aaff5a2b60c562fcf178bbdb4f9bb1c4e008db).
@@ -12,7 +12,7 @@ git2 = "0.10"
## Rust version requirements
git2-rs works with stable Rust, and typically works with the most recent prior
-stable release as well. Check [azure-pipelines.yml](azure-pipelines.yml) to see the oldest
+stable release as well. Check [GitHub Actions](https://github.com/rust-lang/git2-rs/actions) to see the oldest
version of Rust known to pass tests.
## Version of libgit2
