Update pull_request_template.md (#287)

pull_request_template: update template to reflect correct form

Author: samthanawalla

.github/pull_request_template.md

@@ -1,12 +1,28 @@
-### PR Tips
+### PR Guideline
 
 Typically, PRs should consist of a single commit, and so should generally follow
-the [rules for Go commit messages](https://go.dev/wiki/CommitMessage), with the following
-changes and additions:
+the [rules for Go commit messages](https://go.dev/wiki/CommitMessage).
 
-- Markdown is allowed.
+You **must** follow the form:
 
-- For a pervasive change, use "all" in the title instead of a package name.
+```
+net/http: handle foo when bar
+
+[longer description here in the body]
+
+Fixes #12345
+```
+Notably, for the subject (the first line of description):
 
+- the name of the package affected by the change goes before the colon
+- the part after the colon uses the verb tense + phrase that completes the blank in, “this change modifies this package to ___________”
+- the verb after the colon is lowercase
+- there is no trailing period
+- it should be kept as short as possible
+
+Additionally:
+
+- Markdown is allowed.
+- For a pervasive change, use "all" in the title instead of a package name.
 - The PR description should provide context (why this change?) and describe the changes
   at a high level. Changes that are obvious from the diffs don't need to be mentioned.