docs: add session hook to ssi guide (#623)

docs/docs/guides/sign-in-with-github-google-facebook-linkedin.mdx

@@ -16,6 +16,25 @@ Run the [Quickstart](../quickstart.mdx) with Docker Compose:
 $ make quickstart
 ```
 
+:::info
+
+It is very important to add the "session" hook to the after oidc registration
+hooks. Otherwise your users need to use the login flow again to be able to get a
+session.
+
+```yaml title="path/to/my/kratos/config.yml"
+# $ kratos -c path/to/my/kratos/config.yml serve
+selfservice:
+  flows:
+    registration:
+      after:
+        oidc:
+          hooks:
+            - hook: session
+```
+
+:::
+
 ## GitHub
 
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