docs: add migrating to v5 topic

Author: jankapunkt

docs/index.rst

@@ -85,5 +85,6 @@ See the :doc:`/model/spec` of what is required from the model passed to :doc:`/a
 
    misc/extension-grants
    misc/pkce
+   misc/migrating-v5
    misc/migrating-v2-to-v3
 

docs/misc/migrating-to-v5.rst

@@ -0,0 +1,44 @@
+===========================
+ Migrating to 5.x
+===========================
+
+This guide covers the most breaking changes, in case you updated from an earlier version.
+
+-------------------
+Requires Node >= 16
+-------------------
+
+Due to Node 14 reaching end of life (EOL; which implies no security updates) this version requires at least Node 16.
+Future versions of the 5.x major releases will update to a newer Node LTS, once the current one reaches EOL.
+
+Note, that we also won't regard any security patches to problems that are a direct consequence of
+using a Node version that reached EOL.
+
+------------------------
+Removed callback support
+------------------------
+
+With beginning of release 5.0.0 this module dropped all callback support and uses `async/await`
+for all asynchronous operations.
+
+This implies you either need to have a more recent Node.js environment that natively supports `async/await`
+or your project uses tools to support at least Promises.
+
+-----------------
+Update your model
+-----------------
+
+The model functions is now expected to return a Promise (or being declared as `async function`),
+since callback support is dropped.
+
+Note: Synchronous model functions are still supported. However, we recommend to use Promise or async,
+if database operations (or other heavy operations) are part of a specific model function implementation.
+
+------------------
+Scope is now Array
+------------------
+
+In earlier versions we allowed `scope` to be strings with words, separated by empty space.
+With beginning of 5.0.0 the scope parameter needs to be an Array of strings.
+
+This implies to requests, responses and model implementations where scope is included.