updated documentation - cleared up how to migrate an old provider schema

docs/docs/provider_schema.md

@@ -299,4 +299,54 @@ You have the option to retain the existing schema, translate specific properties
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-```
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+```
+
+
+### Migrating from an older version prior to 1.0.1
+
+Before version 1.0.1, provider schemas included definitions for verb groups, which in turn included the available verbs and objects.
+Also, user consent creation was not tied to groups but instead to individual verbs.
+
+A high-level example of an old schema might look like this:
+```json
+{
+  "id": "moodle-0",
+  "name": "Moodle",
+  "description": "Open-source learning management system",
+  "groups": [
+    {
+      "id": "default_group",
+      "label": "Default group",
+      "description": "default",
+      "showVerbDetails": true,
+      "purposeOfCollection": "Lorem Ipsum",
+      "verbs": [
+        ...
+      ]
+    }
+  ],
+  "essentialVerbs": []
+}
+```
+
+To correct an old schema by hand, one would have to extract all verbs from their respective groups and add them to a global "verbs" key in the schema, removing the old "groups" key.
+Essential verbs have kept their structure, but you will have to make sure that the additionalLrs key exists.
+
+The resulting schema would thus have this structure:
+```json
+{
+  "id": "moodle-0",
+  "name": "Moodle",
+  "description": "Open-source learning management system",
+  "verbs": [
+    ...
+  ],
+  "essentialVerbs": [],
+  "additionalLrs": []
+}
+```
+
+After uploading the updated schema, the groups have to be created manually.
+
+
+To automate this process, one could upload the old provider schema in an older version of polaris (pre-1.0.1) and then run all the remaining migrations including `providers/migrations/0008_verb_remove_providerschema_essential_verbs_and_more.py`.  
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