MAHOUT-1980 Add Tutorial for Contributing Algorithms

[rawkintrevo]

Purpose of PR:

Please give a short description of what this PR is for.

A tutorial for new users wishing to contribute an algorithm.

Important ToDos

Please mark each with an "x"

• A JIRA ticket exists (if not, please create this first)[https://issues.apache.org/jira/browse/ZEPPELIN/]
• Title of PR is "MAHOUT-XXXX Brief Description of Changes" where XXXX
  is the JIRA number.
• Created unit tests where appropriate
• Added licenses correct on newly added files
• Assigned JIRA to self
• Added documentation in scala docs/java docs, (and website once that
  is merged to dev)
• Successfully built and ran all unit tests, verified that all tests
  pass locally.

If all of these things aren't complete, but you still feel it is
appropriate to open a PR, please add [WIP] after MAHOUT-XXXX before the
descriptions- e.g. "MAHOUT-XXXX [WIP] Description of Change"

Oh by the way, does this change break earlier versions?
No

Is this the beginning of a larger project for which a feature branch should be made?
No