Improve installation manual/tutorial.

[bryan-lunt]

• submodules
• about getting GEMSTAT
• about getting/setting up data (why not include some example data?)
• about setting up methods
• about setting up scoring (semi-optional)
• What else?

[bryan-lunt]

• overall explanation of the flow of this program, what it does, etc.

[bryan-lunt]

• creation of ensembles.