Minor improvements to PR template

.github/PULL_REQUEST_TEMPLATE.md

 (Thank you for contributing to Caddy! Please fill this out to help us make the most of your pull request.)
 
-### 1. What issue(s) is this pull request related to?
+### 1. What does this change do, exactly?
 
 
-### 2. What does this change do, exactly?
+### 2. Please link to the relevant issues.
 
 
-### 3. What documentation changes (if any) go along with this PR?
+### 3. Which documentation changes (if any) need to be made because of this PR?
 
 
 ### 4. Checklist
 
 - [ ] I have written tests and verified that they fail without my change
 - [ ] I have squashed any insignificant commits
-- [ ] This change has comments for package types, values, and functions or non-obvious lines of code
+- [ ] This change has comments for package types, values, functions, and non-obvious lines of code
 - [ ] I am willing to help maintain this change if there are issues with it later