Documentation: fix typo from f14c04 and add a link while we're here

CONTRIBUTING.md

@@ -4,8 +4,8 @@ New releases tend to get announced on Twitter with credit to contributors.
 If you want an @mention, make sure to tell us your handle.
 Equally, if you don't want to be mentioned, make sure to tell us that.
 
-If you're looking for something to do some open source work, take a look at the issue tracker. `cljs-ajax` always has a lot of issues marked welcome". Drop a li"PR ne if you're interested in working on anything.
+If you're looking for something to do some open source work, take a look at the issue tracker. `cljs-ajax` always has a lot of [issues marked "PR welcome"](https://github.com/JulianBirch/cljs-ajax/issues?q=is%3Aissue+is%3Aopen+label%3A%22PR+welcome%22). Drop a line if you're interested in working on anything.
 
 After that `lein run-tests` should run the tests.
 
-If you just think the documentation needs improving, please send a PR. We've accepted over 100 documentation PRs already. 
+If you just think the documentation needs improving, please send a PR. We've accepted over 100 documentation PRs already.