Add compatibility docs

docs/index.rst

@@ -19,6 +19,7 @@ in alpha. For more information about Takahē, see
    contributing
    domains
    moderation
+   intercompatibility
    stator
    tuning
    releases/index

docs/intercompatibility.rst

@@ -0,0 +1,39 @@
+Intercompatibility
+==================
+
+Takahē aims to be compatible with every modern Fediverse server, but the range
+of options means that we cannot exhaustively test with everything.
+
+This page tracks what we have tried and know works, what has known issues, and
+what we know doesn't work.
+
+
+Full Support
+------------
+
+These servers are our primary testbed and we support them as far as Takahē's
+:doc:`own featureset <features>` allows:
+
+* Mastodon 4.0 and higher
+
+
+Partial Support
+---------------
+
+These servers have been tried and appear to initally work, but more testing is
+needed:
+
+* Akkoma
+* Gotosocial
+* Peertube
+* Pixelfed
+* Pleroma
+
+
+Known Issues
+------------
+
+These servers have the beginnings of support but known bugs that need fixing:
+
+* Mitra
+   * Sends Follow Accept messages in a compact format we don't accept yet