Remove comments about rebasing vs merging; link to longer RTD document

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
index 586536c..55b5964 100644
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
@@ -24,4 +24,4 @@
   - please structure your PR into a series of small commits, each of which does one thing
 * No force-push
   - please do not force-push to update your PR - just add new commit(s)
-  - use `git merge` (or the GitHub web interface) to resolve conflicts - not `git rebase`
+* See our [Guidelines for Contributors](https://mbed-tls.readthedocs.io/en/latest/reviews/review-for-contributors/) for more details about the review process.