Puppet37

Edits to address 3.7 doc tickets: 
DOCS-1137
DOCS-1130
DOCS-1148
Now that I'm looking at this, I think we can actually delete THIS, too! What do you think about reducing this whole section to:

    Node definitions should go in [the main manifest][sitepp]. The main manifest can be a single file, or 
    a directory containing many files.