Improve the pull request template

- hides the instructions in the rendered markdown output
- makes the "Check to confirm" recognized as a tickbox
- space after the "GTMetrix Report" to help position the cursor when inserting the link

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,8 @@
+<!--
 **Important:** Please read all instructions carefully.
 
 _Select the appropriate category for what this PR is about_
+-->
 
 This PR is:
 
@@ -11,7 +13,9 @@ This PR is:
 - [ ] Website code changes (512kb.club site)
 - [ ] Other not listed
 
+<!--
 *Do not tick a checkbox if you haven’t performed its action.* Honesty is indispensable for a smooth review process.
+-->
 
 - [ ] I used the uncompressed size of the site
 - [ ] I have included a link to the GTMetrix report
@@ -21,7 +25,7 @@ This PR is:
 
 ***I confirm that I have read the [FAQ section](https://512kb.club/faq), particularly the two red items around minimal pages and inappropriate content and I attest that this site is neither of these things.***
 
-[ ] Check to confirm
+- [ ] Check to confirm
 
 ```
 - domain:
@@ -30,4 +34,4 @@ This PR is:
   last_checked:
 ```
 
-GTMetrix Report:
+GTMetrix Report: