Updated User Registration API (markdown)

User-Registration-API.md

@@ -19,11 +19,13 @@ Takes a `application/json` payload. The JSON can be one of the following types:
   display_name : <preferred user name>,
   full_name : <customer full name>,
   postcode : <customer postcode>,
-  age_range : <age range key>,
+  year_of_birth : <customer year of birth>,
   password : <password (used for login)>
 }
 ```
 
+Where `year_of_birth` is between 10 and 150 years in the past.
+
 #### Organisation Registration
 
 ```