docs: Improve PR template guidance (#5757)

Co-Authored-By: roman <roman.zavarnitsyn@sentry.io>

Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>

Author: sentry-junior[bot]

.github/pull_request_template.md

@@ -1,5 +1,5 @@
 ## :scroll: Description
-<!--- Describe your changes in detail -->
+<!--- Describe your changes in detail and optionally add screenshots -->
 
 
 ## :bulb: Motivation and Context
@@ -12,6 +12,10 @@
 -->
 
 ## :green_heart: How did you test it?
+<!---
+Include a link to Sentry when applicable:
+* Link to Sentry: <LINK>
+-->
 
 
 ## :pencil: Checklist