ARROW-4332: [Website] Improve documentation for publishing site
ARROW-4332: [Website] Improve documentation for publishing site

Author: Andy Grove <andygrove73@gmail.com>
Author: Wes McKinney <wesm+git@apache.org>
Author: Krisztián Szűcs <szucs.krisztian@gmail.com>

Closes #3498 from andygrove/ARROW-4332 and squashes the following commits:

350fabdf <Wes McKinney> md formatting
07250eb6 <Andy Grove> remove duplicate instruction
54403799 <Andy Grove> Improve documentation for publishing the site
39929d7a <Andy Grove> Merge remote-tracking branch 'upstream/master'
17ee1596 <Andy Grove> Merge remote-tracking branch 'upstream/master'
88267899 <Krisztián Szűcs> ARROW-4273:  Fix verification script to use cf201901 conda-forge label

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