[Hacktoberfest] Migrating wiki documentation

[Dan-Heath]

This PR copies Mesos documentation from the plugin-wiki-docs repo to the mesos-plugin repo as part of the Hacktoberfest docs-to-code project. It includes the following changes:

• Merged wiki Readme information with the existing Readme in the mesos-plugin repo. The only information missing was a URL to the Mesos project web site. The existing Readme in GitHub otherwise looks good to me.
• Extracted change logs to a separate CHANGELOG.md file.
• Modified the URL documentation page reference in the gradle.build file so it points to GitHub.

Please let me know if you have any questions.

• [X] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [X] Ensure that the pull request title represents the desired changelog entry
• [X] Please describe what you did

[Dan-Heath]

Hello @kaiwalyajoshi , @jeschkies , @maselvaraj , @vinodkone , @Vlatombe , I created this PR as part of the Hacktoberfest docs-to-code project. I think it is ready for review, please let me know if you have any questions or would like me to make any changes.

One thing I noticed is the change log contains some instances of the word "slave". Please let me know if you'd like me to change these to "agent" per the naming conventions. Thank you!

[jeschkies]

@kaiwalyajoshi do you think we should make a 2.0 release?

[kaiwalyajoshi]

@jeschkies There's a 2.0 release that was pushed out to Jenkins plugins repository: https://plugins.jenkins.io/mesos/#releases We used it for the USI based Jenkins 4.0 release here: https://github.com/mesosphere/dcos-jenkins-service/blob/c6dee302864fbeb5dddaedfc981e6013c39e5042/plugins.conf#L22

Are you referring to a 2.0 release here on Github?

I guess we should also release a 1.0 and other ones then.

[stale[bot]]

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