Add links to PR template

People are lazy and would read it otherwise
I also renamed `integration` -> `e2e` because it was confusing

.github/pull_request_template.md

@@ -8,16 +8,16 @@ Choose the right checklist for the change that you're making:
 
 - [ ] Related issues linked using `fixes #number`
 - [ ] Integration tests added
-- [ ] Errors have a helpful link attached, see `contributing.md`
+- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
 
 ## Feature
 
 - [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
 - [ ] Related issues linked using `fixes #number`
-- [ ] Integration tests added
+- [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added
 - [ ] Documentation added
 - [ ] Telemetry added. In case of a feature if it's used or not.
-- [ ] Errors have a helpful link attached, see `contributing.md`
+- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
 
 ## Documentation / Examples