Move `MAINTAINERS` to the root folder (#7528)

CONTRIBUTING.adoc

@@ -144,7 +144,7 @@ To submit a pull request:
 . Wait for CI results/reviews, process the feedback.
 * If you do not get feedback after 3 days, feel free to ping `@jenkinsci/core-pr-reviewers` in the comments.
 * Usually we merge pull requests after 2 approvals from reviewers, no requested changes, and having waited some more time to give others an opportunity to provide their feedback.
-  See link:/docs/MAINTAINERS.adoc[this page] for more information about our review process.
+  See link:MAINTAINERS.adoc[this page] for more information about our review process.
 
 Once your Pull Request is ready to be merged,
 the repository maintainers will integrate it, prepare changelogs, and

docs/MAINTAINERS.adoc → MAINTAINERS.adoc

@@ -307,7 +307,7 @@ triage team members are not responsible for handling the ticket after initial tr
 Other materials which might help:
 
 * link:https://www.jenkins.io/participate/code/[Contribute to Jenkins / Code] or 
-  link:https://github.com/jenkinsci/jenkins/blob/master/CONTRIBUTING.md[Contributing to the Jenkins Core] - 
+  link:CONTRIBUTING.adoc[Contributing to the Jenkins Core] - 
   extended version of "feel free to contribute".
 * link:https://github.com/jenkinsci/.github/blob/master/SUPPORT.md[Jenkins Support Disclaimer Page] -
 for those requesters who expect quick response and SLA.

README.adoc

@@ -52,11 +52,11 @@ Our latest and greatest source of Jenkins can be found on https://github.com/jen
 
 == Contributing to Jenkins
 
-Follow the link:CONTRIBUTING.md[contributing guidelines] if you want to propose a change in the Jenkins core.
+Follow the link:CONTRIBUTING.adoc[contributing guidelines] if you want to propose a change in the Jenkins core.
 For more information about participating in the community and contributing to the Jenkins project,
 see https://www.jenkins.io/participate/[this page].
 
-Documentation for Jenkins core maintainers is in the link:docs/MAINTAINERS.adoc[maintainers guidelines].
+Documentation for Jenkins core maintainers is in the link:MAINTAINERS.adoc[maintainers guidelines].
 
 == News and Website