docs: Fix formatting and remove outdated advice

Note that the alignment advice is problematic. Not each line needs to be
left aligned, but it is true that no line should go further left than
the initial line. The part about not forgetting | becomes a bit
redundant as we have schema validation now that will make sure it is set
to be a string.

Author: consideRatio

doc/zero-to-binderhub/setup-binderhub.rst

@@ -48,25 +48,18 @@ need to insert. Note that the first line is not indented at all::
     # paste the content after `password: |` below
     password: |
       {
-      "type": "<REPLACE>",
-      "project_id": "<REPLACE>",
-      "private_key_id": "<REPLACE>",
-      "private_key": "<REPLACE>",
-      "client_email": "<REPLACE>",
-      "client_id": "<REPLACE>",
-      "auth_uri": "<REPLACE>",
-      "token_uri": "<REPLACE>",
-      "auth_provider_x509_cert_url": "<REPLACE>",
-      "client_x509_cert_url": "<REPLACE>"
+        "type": "<REPLACE>",
+        "project_id": "<REPLACE>",
+        "private_key_id": "<REPLACE>",
+        "private_key": "<REPLACE>",
+        "client_email": "<REPLACE>",
+        "client_id": "<REPLACE>",
+        "auth_uri": "<REPLACE>",
+        "token_uri": "<REPLACE>",
+        "auth_provider_x509_cert_url": "<REPLACE>",
+        "client_x509_cert_url": "<REPLACE>"
       }
 
-
-.. tip::
-
-   * The content you put just after ``password: |`` must all line up at the same
-     tab level.
-   * Don't forget the ``|`` after the ``password:`` label.
-
 If you are using Docker Hub
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~