Add changelog guidelines in the PR template

Author: hculea

.github/pull_request_template.md

@@ -38,7 +38,13 @@ This will serve as a starting point for your reviewers, for functional testing.
 A one line sentence describing the change that this PR introduces. 
 If this has impact over the user experience, your changelog will be included in the release notes of the next stable version of 1Password CLI.
 
-Have a look over 1Password CLI's past release notes for a some examples: 
+Here are a few guidelines for writing a good changelog:
+- Keep your description to a single sentence if you can, and use proper capitalization and punctuation, including a final period.
+- Don't use emoji in your description.
+- Avoid starting your sentence with "improved" or "fixed", especially when using those change types. Instead, describe the improvement or say what you fixed.
+- Avoid using terminology like "Users are shown" or "You can now" and instead focus on the thing that was changed.
+
+Have a look over 1Password CLI's past release notes for examples: 
 https://app-updates.agilebits.com/product_history/CLI2
 -->