update(docs): add install method for early adopters

Author: Guts

docs/usage/installation.md

@@ -7,3 +7,22 @@ This plugin is published on the official QGIS plugins repository: <https://plugi
 ## Beta versions released
 
 Enable experimental extensions in the QGIS plugins manager settings panel.
+
+## Earlier development version
+
+If you define yourself as early adopter or a tester and can't wait for the release, the plugin is automatically packaged for each commit to main, so you can use this address as repository URL in your QGIS extensions manager settings:
+
+```url
+https://github.com/WhereGroup/profile_manager/releases/latest/download/plugins.xml
+```
+
+In QGIS:
+
+1. Menu `Plugins` > `Install/Manage Plugins`
+2. `Settings` tab
+3. Below the repositories list, click `Add...` and enter the URL above
+4. Once the repository is added, the plugin should appear in the `Not installed` tab.
+
+:::{warning}
+Selon votre configuration, redémarrer QGIS peut être nécessaire, le gestionnaire d'extensions ayant des comportements parfois capricieux par rapport aux dépôts tiers.
+:::