Move synctl into synapse._scripts and expose as an entrypoint (#12140)

docs/upgrade.md

@@ -47,7 +47,7 @@ this document.
     3.  Restart Synapse:
 
         ```bash
-        ./synctl restart
+        synctl restart
         ```
 
 To check whether your update was successful, you can check the running
@@ -85,6 +85,27 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.55.0
+
+## `synctl` script has been moved
+
+The `synctl` script
+[has been made](https://github.com/matrix-org/synapse/pull/12140) an
+[entry point](https://packaging.python.org/en/latest/specifications/entry-points/)
+and no longer exists at the root of Synapse's source tree. If you wish to use
+`synctl` to manage your homeserver, you should invoke `synctl` directly, e.g. 
+`synctl start` instead of `./synctl start` or `/path/to/synctl start`. 
+
+You will need to ensure `synctl` is on your `PATH`.
+  - This is automatically the case when using
+    [Debian packages](https://packages.matrix.org/debian/) or
+    [docker images](https://hub.docker.com/r/matrixdotorg/synapse)
+    provided by Matrix.org.
+  - When installing from a wheel, sdist, or PyPI, a `synctl` executable is added 
+    to your Python installation's `bin`. This should be on your `PATH`
+    automatically, though you might need to activate a virtual environment
+    depending on how you installed Synapse.
+
 # Upgrading to v1.54.0
 
 ## Legacy structured logging configuration removal