Docs

[jwdebelius]

Updates and fixes documentation:

• Expands installation guide under the assumption that someone will be confused about which R they should be using to install the package
• Expands tutorial documentation and adds a first-pass visualization option for those who like to visualization within qiime
• Defines the coefficients (addressees #1)
• Hides global (skips over #3)

[mortonjt]

Looking good! Thanks @jwdebelius !