[release-notes] Add README pointing to release notes contribution guidelines

[Michael Catanzaro <mcatanzaro src gnome org>]

commit adc62fc47454873af29e6a9f922e93a965084b99
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Thu Sep 3 08:54:31 2020 -0500

    Add README pointing to release notes contribution guidelines

 README.md | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/README.md b/README.md
new file mode 100644
index 00000000..d9685a14
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# Contribution guidelines
+
+Please read [instructions for contributing to release notes](https://wiki.gnome.org/ReleaseNotes).