RELEASE_NOTES: Based on the version from 5.1

Name taken to match the suggested news posted by lynne

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

RELEASE_NOTES

@@ -0,0 +1,15 @@
+
+            ┌──────────────────────────────────────────┐
+            │ RELEASE NOTES for FFmpeg 6.1 "Heaviside" │
+            └──────────────────────────────────────────┘
+
+   The FFmpeg Project proudly presents FFmpeg 6.1 "Heaviside", about 8
+   months after the release of FFmpeg 6.0.
+
+   A complete Changelog is available at the root of the project, and the
+   complete Git history on https://git.ffmpeg.org/gitweb/ffmpeg.git
+
+   We hope you will like this release as much as we enjoyed working on it, and
+   as usual, if you have any questions about it, or any FFmpeg related topic,
+   feel free to join us on the #ffmpeg IRC channel (on irc.libera.chat) or ask
+   on the mailing-lists.