add upgrading readme with basic how to upgrade, and patch

Author: jay-oswald

README.md

@@ -68,10 +68,10 @@ Features not yet implemented:
 
 | Moodle version    | Branch             | PHP       | SimpleSAMLphp |
 | ----------------- | ------------------ |-----------|---------------|
-| Moodle 4.5        | `MOODLE_405_STABLE`| 8.1+      | v2.3.5        |
+| Moodle 4.5        | `MOODLE_405_STABLE`| 8.1+      | v2.3.7        |
 | Moodle 4.4        | `MOODLE_404_STABLE`| 8.1+      | v2.3.5        |
 | Moodle 3.9 to 4.3 | `MOODLE_39_STABLE` | 7.4+      | v2.0.5        |
-| Totara 19+        | `TOTARA_19` | 7.4+      | v2.0.5        |
+| Totara 19+        | `TOTARA_19`        | 7.4+      | v2.0.5        |
 | Totara 13+        | `TOTARA_13_STABLE` | 7.4+      | v2.0.5        |
 
 ## Installation

UPGRADING.md

@@ -0,0 +1,12 @@
+# Upgrading
+Older branches have simplesamlphp included in `.extlib` folder, see `UPGRADE.md` in that folder for instructions.
+
+Newer versions we are using composer to install and update simplesamlphp, which is what the rest of this section is about.
+
+There has been a `Dockerfile` and `docker-compose.yaml` added to allow running composer update consistently without relying on local configuration of php.
+
+To run an upgrade running `docker compose up` will start the container and run `composer update --no-dev`. You can then commit the result with the updated `vendor` folder and updated `composer.lock` file.
+
+
+# Patches
+We are using composer patches to manage any changes needed for simplesamlphp, or any other composer packages. To do this you must generate a [git patch](https://git-scm.com/docs/git-format-patch), add it to the `patches/` folder, and reference it in the list in `composer.json`.