chore: adding template instructions and updating how we update our changelogs (#649)

* Removing changelog from package and updating it with real changes for that particular package
Adding real changelog for the whole project at the root of the project
Updating the PR template with reminders to update tests and changelogs

* adding current changelog

Author: SamuelBellomo

.github/PULL_REQUEST_TEMPLATE.md

@@ -12,7 +12,10 @@
 -->
 
 ### Contribution checklist
+ - [ ] Tests have been added for boss room and/or utilities pack
+ - [ ] Release notes have been added to the [project changelog](../CHANGELOG.md) file and/or [package changelog](../Packages/com.unity.multiplayer.samples.coop/CHANGELOG.md) file
  - [ ] Pull request has a meaningful description of its purpose
  - [ ] All commits are accompanied by meaningful commit messages
  - [ ] JIRA ticket ID is in the PR title or at least one commit message
  - [ ] Include the ticket ID number within the body message of the PR to create a hyperlink
+