matrix-spec-proposals

cea6622d - Clarify that implementations can use stable prefixes once an MSC has merged (#3179)

Clarify that implementations can use stable prefixes once an MSC has merged (#3179) Fixes #3146. This PR changes the Matrix Spec Proposals page to clarify that implementations **do not** need to wait until a spec release to use stable prefixes, but that they can do so after the corresponding MSC has been merged. The justification is that once an MSC has been merged, it's fairly guaranteed that it will land in the spec. Yet it will take time for the spec release process to run its course, and we shouldn't make implementations wait for that. The exception to this is if implementating a feature in a backwards-compatible way requires a new spec version to indicate to clients/servers that a feature has been added/changed. This situation is rare though, and most implementations won't fall into this category.