Add documentation for ANDROID_IGNORED_VARIANTS

**Is your feature request related to a problem? Please describe.**

I just found the `dependency.analysis.android.ignored.variants` gradle.properties flags, which allows my very memory-hungry build to ignore a bunch of variants that we don't need or want to analyze. However, I wasn't able to find documentation for this in the wiki: https://github.com/autonomousapps/dependency-analysis-gradle-plugin/wiki

**Describe the solution you'd like**

Would be nice if you could document that flag and how to use! Some android developers may not know exactly what a `variant` is, although I imagine if they've found this plugin they have some basic knowledge.

**Describe alternatives you've considered**

N/A

**Additional context**

Thanks for making this plugin!

Start by reviewing the project wiki, especially the existing Gradle properties documentation, and locate the dependency.analysis.android.ignored.variants flag. Done means the wiki explains what the flag does, how to configure it, and what an Android variant is for readers who may be unfamiliar with the term.

Written by the indexing model from the issue text.