interfaces: warn about api key uniqueness

Created by: lynxlynxlynx

just one case here: https://civicrm.stackexchange.com/questions/4289/error-no-cms-user-associated-with-given-api-key

docs/api/interfaces.md

@@ -222,6 +222,9 @@ Response to creating a new contact
 
 Before being able to use the REST Interface you will need to have set up the `CIVICRM_SITE_KEY` and the users `API_KEY`. There are three methods of creating API keys for users
 
+!!! warning
+    API keys need to be unique and set on a user with appropriate [permissions](/security/permissions.md).
+
 #### Manual Method
 
 You can enter the key directly in the database. This would be done by the following

[homotechsual]

Created by: lynxlynxlynx

This is the syntax already used for notes, warnings and fatal errors. Why do you suggest a change?

[homotechsual]

Created by: lynxlynxlynx

Eg. check just below this headline from the same page: https://docs.civicrm.org/dev/en/latest/api/interfaces/#crmapi3 Code formatting isn't fitting here.