Added JGraphT Algorithm Package Summary

[Ru-816]

I have created a text file, using markdown extension, where I have summarized the purpose of every algorithm contained in alg package, inside the jgrapht-core package. I did this change in order to clarify the usage of JGraphT algorithms for users.

• I read and understood https://github.com/jgrapht/jgrapht/wiki/Become-a-Contributor
• I read and understood https://github.com/jgrapht/jgrapht/wiki/How-to-make-your-first-%28code%29-contribution
• I added unit tests
• I added documentation
• I followed the Coding and Style Conventions
• I have not modified HISTORY.md or CONTRIBUTORS.md
• I ensured that the git commit message is a good one

[jsichi]

Thank you for the contribution. Here are a couple of initial review comments:

1. This information would be better placed in the package-info.html (which is currently a stub), meaning it would need to be HTML inside the Javadoc. We already have an automatically generated summary as part of the core Javadoc at https://jgrapht.org/javadoc/org.jgrapht.core/module-summary.html, but the details you've added at the alg level would be nice. In the HTML, be sure to use @link tags to reference the algorithm examples.

2. Avoid specifying the exact number of algorithms ("4 algorithms related to...") because this is guaranteed to become out of date when someone adds a new algorithm later. Even if there's only one, just say "contains algorithms related to..."

I'll have some more detailed comments after these are addressed.