[MNGSITE-364] Improve the CI Friendly Documentation

**[Aaron Digulla](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=digulla)** opened **[MNGSITE-364](https://issues.apache.org/jira/browse/MNGSITE-364?redirect=false)** and commented

Please improve the page at https://maven.apache.org/maven-ci-friendly.html

I think the document explains an important feature but I find it confusing.
* Why would someone want to use this feature? Which problems does it solve and which are created?
* How will Maven determine the values for ${sha1} and ${changelist}?
* You mention

1.0.0-${buildNumber}-SNAPSHOT"will _not work as expected_". Why not? Explain why the build number doesn't make as much sense as the other variables.
* In the section "Dependencies" why not use `dependencyManagement`?
* Under "Install / Deploy", you say "will not be consumable by Maven anymore". Why?

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No further details from [MNGSITE-364](https://issues.apache.org/jira/browse/MNGSITE-364?redirect=false)

Start with the Maven CI Friendly page at https://maven.apache.org/maven-ci-friendly.html and review the sections on the feature's purpose, ${sha1} and ${changelist}, Dependencies, and Install / Deploy. Done means the page answers each listed question, including why buildNumber is unsuitable and why the stated install/deploy result occurs.

Written by the indexing model from the issue text.