Update PR template to use absolute links (#4341)

* Update PR template to use absolute links

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

.github/PULL_REQUEST_TEMPLATE.md

@@ -3,5 +3,5 @@
 <!-- Please read CONTRIBUTING.rst before submitting your pull request -->
 
 * [ ] Pull request is based on the develop branch
-* [ ] Pull request includes a [changelog file](CONTRIBUTING.rst#changelog)
-* [ ] Pull request includes a [sign off](CONTRIBUTING.rst#sign-off)
+* [ ] Pull request includes a [changelog file](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#changelog)
+* [ ] Pull request includes a [sign off](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#sign-off)

changelog.d/4341.misc

@@ -0,0 +1 @@
+Update pull request template to use absolute links