Add notice about rebase

This is a temporary notice about our massive rebase effort. Pull
requests based off 'main' will no longer be accepted, only if they are
based against 'audacity-3.7-rebase' (the rebase branch). Thus, add a
note to the README and contributing policy about it.

Once the rebase is complete, and we merge 'audacity-3.7-rebase' into
main, we will continue working on the main branch as normal.

Signed-off-by: Avery King <[email protected]>

CONTRIBUTING.md

@@ -4,6 +4,21 @@ Thanks for showing your interest to contribute, your contribution is very
 valuable to us as people like **you** help us build Tenacity. Some guidelines
 have been put in place in an effort to keep the codebase clean.
 
+**At this time, we are halting acceptance of new pull requests against the
+`main` branch due to a large effort to rebase off Audacity 3.7.1. At the time
+of writing, things are going smoothly so far. View PR
+https://codeberg.org/tenacityteam/tenacity/pulls/527 to see the progress on the
+rebase**.
+
+**During the rebase, the rebase branch, `audacity-3.7-rebase`, will temporarily
+become the default branch. Please base your PR off the `audacity-3.7-rebase`
+branch and open a PR against the same branch. All other rules and procedures
+regarding contributions will still apply as they did before. Thus, replace any
+references to `main` below with `audacity-3.7-rebase`.**
+
+**This notice (in bold) is temporary. Once removed, we will accept
+contributions as we did before the rebase again.**
+
 ## Reporting bugs and feature requests
 
 Our IRC channel, [`#tenacity` on Libera](https://web.libera.chat/#tenacity)

README.md

@@ -1,3 +1,9 @@
+**We are currently undergoing a major rebase off Audacity 3.7.1. See PR https://codeberg.org/tenacityteam/tenacity/pulls/527 for progress. During this time, we will NOT accept pull requests against `main`. Please (re)base them off the `audacity-3.7-rebase` branch instead.**
+
+For more information on the situation, please see https://fosstodon.org/@tenacity/113731514298404501. We are still accepting contributions elsewhere. We resume accepting contributions when the rebase is complete. Thank you for your understanding.
+
+---
+
 [![Tenacity](https://codeberg.org/tenacityteam/assets/raw/branch/master/PNG/tenacity-logo-dark-readme.png)](https://tenacityaudio.org)
 
 [![Chat on IRC](https://badgen.net/badge/irc/%23tenacity/green)](https://web.libera.chat/gamja/?channels=#tenacity)