DOC-1281 Puppet Server puppet_conf_setting_diffs edit

Edited puppet_conf_setting_diffs.markdown
DOC-1281: Edits to puppet_conf_setting_diffs.

Title change, fixed style on file names (`puppet.conf` -> puppet.conf), and fixed awkward usage error.
Merge pull request #315 from jbondpdx/conf-setting-diff

DOC-1281 Puppet Server puppet_conf_setting_diffs edit