github: Add a Generative AI Usage declaration to the PR template.

Goes along with
https://github.com/micropython/micropython/wiki/ContributorGuidelines#generative-ai-policy

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

.github/pull_request_template.md

@@ -3,7 +3,6 @@
      others can review your Pull Request.
 
      Before submitting, please read:
-     https://github.com/micropython/micropython/blob/master/CODEOFCONDUCT.md
      https://github.com/micropython/micropython/wiki/ContributorGuidelines
 
      Please check any CI failures that appear after your Pull Request is opened.
@@ -12,16 +11,15 @@
 ### Summary
 
 <!-- Explain the reason for making this change. What problem does the pull request
-     solve, or what improvement does it add? Add links if relevant. -->
-
+     solve, or what improvement does it add? Add links if relevant,
+     especially links to open issues. -->
 
 ### Testing
 
 <!-- Explain what testing you did, and on which boards/ports. If there are
      boards or ports that you couldn't test, please mention this here as well.
 
-     If you leave this empty then your Pull Request may be closed. -->
-
+     If you leave this section empty then your Pull Request may be closed. -->
 
 ### Trade-offs and Alternatives
 
@@ -31,3 +29,20 @@
 
      Delete this heading if not relevant (i.e. small fixes) -->
 
+
+### Generative AI
+
+<!-- Please delete the answer below which doesn't apply, or write your own
+     answer with more details. -->
+
+I did not use generative AI tools when creating this PR.
+
+I used generative AI tools when creating this PR, but a human has checked the
+code and is responsible for the code and the description above.
+
+<!-- We require everyone to answer this question. If you delete this section or
+     ignore it then your PR may be closed.
+
+     For more information, consult the MicroPython Generative AI Policy:
+     https://github.com/micropython/micropython/wiki/ContributorGuidelines#generative-ai-policy
+     -->