update RFC5

Author: tomkralidis

docs/development/rfc/5.md

@@ -30,6 +30,8 @@ limits:
     defaultitems: 10  # applies to vector data
     maxitems: 500  # applies to vector data
     maxdistance: [x, y]  # applies to all datasets
+    units: m  # as per UCUM https://ucum.org/ucum#section-Tables-of-Terminal-Symbols
+    on_surpass: error  # one of error, throttle
 ```
 
 The `limits` setting will be applied as follows:
@@ -43,6 +45,8 @@ The `limits` setting will be applied as follows:
 
 An `evaluate_limit` function will be added to the `pygeoapi` module for use by `pygeoapi.api` accordingly.
 
+If `limits.on_surpass` is `error`, then pygeoapi will throw HTTP 413
+
 ### Backwards Compatibility Issues
 
 The `limits` setting fully replaces `server.limit` and represents a compatibility break.  The new functionality will not be backported to other branches.