Updated the service integration section of Mattermost documentation (!718) · Merge requests · GitLab.org / omnibus-gitlab · GitLab

Do not update/delete: Banner broadcast message test data

Do not update/delete: Notification broadcast message test data

username-removed-39414 requested to merge aral/omnibus-gitlab:patch-1 into master Apr 06, 2016

Adds prerequisite step of enabling incoming webhooks.
Updates menu names in instructions to those matching the actual menu names in the latest release.
Minor typographical change to use actual arrows instead of greater-than symbols in instructions.