Update README.md

Modified JSON to YAML, and added a note about installing HAProxy

Includes fix from @rstrox about trailing commas in example YAML

Closes #77
Implement EC2 tag watcher.
Initial stab at tests for EC2 tag watcher.
Validate server_port_override
Merge pull request #80 from airbnb/tag_watcher

Tag watcher
[readme] better document shared_frontend and port options

also fixes some stylistic nits
Consider only running instances and memoize AWS calls.

It doesn't make sense to retrieve starting, stopping, stopped, and terminated instances
and include them on the server list. The `memoize` block ensures that results
from requests are remembered, avoiding redundant calls to retrieve instance
details.
Merge pull request #85 from strava/ls/filter_ec2_instances

Consider only running instances and memoize AWS calls.
synapse etcd service watcher
Add etcd to Gemfile.lock
Split large method up, support recursion through subdirs
Make recursion work
Make the watcher into a thread
Only reconfigure if new backends are discovered
Fix bug stopping backends ever registering
Fix bug with logic being wrong way around
Remove my monkeypatch for etcd