Add a section to the PR template requiring an estimate of complexity …

…and risk (#407)

.github/pull_request_template.md

@@ -1,7 +1,6 @@
 # Description of Changes
 
 
-
 # API and ABI
 
  - [ ] This is a breaking change to the module ABI
@@ -10,3 +9,14 @@
  - [ ] This is a breaking change to the SDK API
 
 *If the API is breaking, please state below what will break*
+
+# Expected complexity level and risk
+
+*How complicated do you think these changes are? Grade on a scale from 1 to 5,
+where 1 is a trivial change, and 5 is a deep-reaching and complex change.*
+
+*This complexity rating applies not only to the complexity apparent in the diff,
+but also to its interactions with existing and future code.*
+
+*If you answered more than a 2, explain what is complex about the PR,
+and what other components it interacts with in potentially concerning ways.*