Updating config options as ENVs in README, updating a few other links

[rgarcia6520]

Signed-off-by: garcia.ryan garcia.ryan@solute.us

Summary

Updating section of README for mattermost team edition to use config values with ENV vars rather than configJSON items per issue #238 . Also updating a few other broken links.

Ticket Link

Fixes #238

[mattermod]

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[rgarcia6520]

/check-cla

[mattermod]

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[flickerfly]

Any reviewers about that could give this a quick look?