Docs notes on releasing 4.0 (#7264)

Co-authored-by: Alan Cruickshank <alan+git@a14k.co.uk>
Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

docs/source/index.rst

@@ -18,6 +18,8 @@ Notable releases:
   and the `--force` option was removed. Richer information returned by the
   :code:`sqlfluff lint` command (although in a different structure to previous
   versions). See :ref:`upgrading_3_0`.
+* **4.0.x**: First release with optional rust routines. An install with
+  :code:`sqlfluff[rs]` will now include the rust routines. See :ref:`upgrading_4_0`.
 
 For more detail on other releases, see our :ref:`releasenotes`.
 

docs/source/reference/releasenotes.rst

@@ -10,6 +10,8 @@ of each individual release, see the detailed changelog_.
 
 .. _changelog: https://github.com/sqlfluff/sqlfluff/blob/main/CHANGELOG.md
 
+.. _upgrading_4_0:
+
 Upgrading to 4.x
 ----------------
 
@@ -18,7 +20,13 @@ For most users, no difference will be visible, as currently the rust libraries
 are *opt-in*, and must be explicitly installed with :code:`pip install sqlfluff[rs]`.
 
 Rust libraries are built for most major platforms, and we believe are ready for
-public beta testing, but they should be considered experimental until the 5.x release.
+public beta testing, but they should be considered experimental until the 5.x
+release. Performance gains on initial release are not expected to be significant,
+but we do expect they will be significant once the routines are mature.
+
+Additionally:
+
+* We drop support for dbt 1.4 and older, and include support for dbt 1.10.
 
 .. _upgrading_3_0: