docs: Add checkbox reminder of foundry-zksync-book (#817)

Add checkbox to remind us to update the foundry book

.github/PULL_REQUEST_TEMPLATE.md

@@ -11,7 +11,13 @@
 # Evidence :camera:
 Include screenshots, screen recordings, or `console` output here demonstrating that your changes work as intended
 
+# Documentation :books:
+Please ensure the following before submitting your PR:
+
+- [ ] Check if these changes affect any documented features or workflows.
+- [ ] Update the [book](https://github.com/matter-labs/foundry-zksync-book) if these changes affect any documented features or workflows.
+
 <!-- All sections below are optional. You can uncomment any section applicable to your Pull Request. -->
 
 <!-- # Notes :memo:
-* Any notes/thoughts that the reviewers should know prior to reviewing the code? -->
+* Any notes/thoughts that the reviewers should know prior to reviewing the code? -->