Update README.md

Fix setup instructions.
Manually applying sbt/sbt#1382
globalSettings typo. Closes #1
Manually port over missed updates
link to fm-sbt-s3-resolver. fixes sbt/sbt#1321
Manually applying typo fix. closes sbt/sbt#1331
Merge remote-tracking branch 'origin/master' into wip/use-public-verisons