Add first release note

Seeing as this is the first official release, there aren't really any
"changes", per se. Instead, we simply note that this is the first
initial release.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

releasenotes/notes/initial-release-0aad09064615d023.yaml

@@ -0,0 +1,4 @@
+---
+prelude: >
+    Initial release of `git-pw` using the new REST API provided in Patchwork
+    2.0