[site] add section on making behavior changes

This is long overdue, and we're going to try and make a couple of behavior
changes soon.

site/src/book/stability.md

@@ -12,9 +12,32 @@ The cargo-nextest binary follows [semantic versioning](https://semver.org/), whe
 
 [Experimental features](experimental-features.md) are not part of the public API. They may change or be removed in a patch release.
 
-Within a version series, the public API will be append-only. New options or keys may be added, but existing keys will continue to be as they were. Existing options may be deprecated but will not be removed within a version series.
+Within a version series, the public API will be append-only. New options or keys may be added, but
+existing keys will continue to be as they were. Existing options may be deprecated but will not be
+removed within a version series, except via the policy listed in [Making behavior changes](#making-behavior-changes).
 
-The public API does _not_ include human-readable output generated by nextest, or in general anything printed to stderr.
+The public API does _not_ include human-readable output generated by nextest, or in general anything
+printed to stderr.
+
+### Making behavior changes
+
+In general, the meaning of options will not change and functionality will not be removed from
+cargo-nextest within a version series.
+
+However, in some cases, we may need to make behavior changes to fix a bug or security issue. These
+sorts of changes will be made based on standard semantic versioning rules: bugs will be fixed in
+patch releases, with due consideration given to existing use cases.
+
+We may also need to make behavior changes to address what we consider to be major user interface
+deficiencies. **This will not be done lightly:** the maintainers of nextest understand the
+importance of stable, dependable CLI interfaces.
+
+In those cases, we will follow the following procedure:
+
+1. On the nextest issue tracker, an issue will be filed under the [*behavior-change* label](https://github.com/nextest-rs/nextest/issues?q=is%3Aopen+label%3Abehavior-change+sort%3Aupdated-desc). This issue will outline the motivation, and be used for coordination and feedback.
+2. The behavior will be marked as deprecated and a warning will be provided within the CLI. If applicable, an alternative will be provided in the warning message. If there is no alternative, a configuration option and/or environment variable will be provided to silence the warning.
+3. A timeline to change the behavior will be provided. The timeline will be at least 3 months long to provide ample time for users to adapt to the new behavior.
+4. After that time has elapsed, the behavior will be changed in the following version of nextest.
 
 ## Libraries