github: comment contrib repo change explanation in pull request template

So that the massive explanation is not rendered after PR has been
opened. Comment also the description explanation while we are at it.

.github/pull_request_template.md

@@ -1,6 +1,8 @@
 # Description
 
+<!--
 Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.
+-->
 
 Fixes # (issue)
 
@@ -21,6 +23,7 @@ Please describe the tests that you ran to verify your changes. Provide instructi
 
 # Does This PR Require a Contrib Repo Change?
 
+<!--
 Answer the following question based on these examples of changes that would require a Contrib Repo Change:
 - [The OTel specification](https://github.com/open-telemetry/opentelemetry-specification) has changed which prompted this PR to update the method interfaces of `opentelemetry-api/` or `opentelemetry-sdk/`
 - The method interfaces of `test/util` have changed
@@ -33,6 +36,7 @@ Answer the following question based on these examples of changes that would requ
 - Major changes to project information, such as in:
     - `README.md`
     - `CONTRIBUTING.md`
+-->
 
 - [ ] Yes. - Link to PR: 
 - [ ] No.