Expand env. variable list, misc copy edits

[hramos]

• Add Server Fault link, for deployment and hosting questions.
• Move non-critical options out of Basic options
• Clean up File Adapters section
• Add Support section, encouraging people to use existing communities for support before opening an issue

[codecov-io]

Current coverage is 86.12%

Merging #1086 into master will not affect coverage as of 65863e6

@@            master   #1086   diff @@
======================================
  Files           76      76       
  Stmts         5103    5103       
  Branches      1108    1108       
  Methods          0       0       
======================================
  Hit           4395    4395       
  Partial         13      13       
  Missed         695     695       

Review entire Coverage Diff as of 65863e6

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