Update outdated links in PULL_REQUEST_TEMPLATE.md (#11225)

Author: dklimpel

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,12 +1,13 @@
 ### Pull Request Checklist
 
-<!-- Please read CONTRIBUTING.md before submitting your pull request -->
+<!-- Please read https://matrix-org.github.io/synapse/latest/development/contributing_guide.html before submitting your pull request -->
 
 * [ ] Pull request is based on the develop branch
-* [ ] Pull request includes a [changelog file](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.md#changelog). The entry should:
+* [ ] Pull request includes a [changelog file](https://matrix-org.github.io/synapse/latest/development/contributing_guide.html#changelog). The entry should:
   - Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
   - Use markdown where necessary, mostly for `code blocks`.
   - End with either a period (.) or an exclamation mark (!).
   - Start with a capital letter.
-* [ ] Pull request includes a [sign off](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.md#sign-off)
-* [ ] Code style is correct (run the [linters](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.md#code-style))
+* [ ] Pull request includes a [sign off](https://matrix-org.github.io/synapse/latest/development/contributing_guide.html#sign-off)
+* [ ] [Code style](https://matrix-org.github.io/synapse/latest/code_style.html) is correct
+  (run the [linters](https://matrix-org.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

changelog.d/11225.misc

@@ -0,0 +1 @@
+Replace outdated links in the pull request checklist with links to the rendered documentation.