Documentation: Add how to setup email configuration

Documentation/email-configuration.md

+# Configuring Sending Emails
+
+Dex sends emails to a during the registration process to verify an email
+address belongs to the person signing up. Currently Dex supports two ways of
+sending emails, and has a third option for use during development.
+
+Configuration of the email provider in Dex is provided through a JSON file. All
+email providers have a `type` and `id` field as well as some additional provider
+specific fields.
+
+## SMTP
+
+If using SMTP the `type` field **must** be set to `smtp`. Additionally both
+`host` and `port` are required. If you wish to use SMTP plain auth, then
+set `auth` to `plain` and specify your username and password.
+
+```
+{
+    "type": "smtp",
+    "host": "smtp.example.org",
+    "port": 587,
+    "auth": "plain",
+    "username": "postmaster@example.org",
+    "password": "foo"
+}
+```
+
+## Mailgun
+
+If using Mailgun the `type` field **must** be set to `mailgun`. Additionally
+`privateAPIKey`, `publicAPIKey`, and `domain` are required.
+
+```
+{
+    "type": "mailgun",
+    "privateAPIKey": "key-XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
+    "publicAPIKey": "YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY",
+    "domain": "sandboxZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ.mailgun.org"
+}
+```
+
+## Dev
+
+The fake emailer should only be used in development. The fake emailer
+prints emails to `stdout` rather than sending any email. If using the fake
+emailer the `type` field **must** be set to `fake`.
+
+```
+{
+    "type": "fake"
+}
+```
\ No newline at end of file

Documentation/getting-started.md

@@ -63,7 +63,12 @@ export DEX_OVERLORD_LOG_DEBUG=true
 
 # Start the dex-worker
 
-Now start the worker:
+Before starting `dex-worker` you should determine how you want verification emails to be delivered to the user.
+If you just want to test dex out, you can just use the provided sample config in `static/fixtures/emailer.json.sample`.
+Please review [email-configuration](https://github.com/coreos/dex/blob/master/Documentation/email-configuration.md) for details
+(make sure you point `--email-cfg` to your newly configured file).
+
+Once you have setup your email config run `dex-worker`:
 
 `./bin/dex-worker --db-url=$DEX_DB_URL --key-secrets=$DEX_KEY_SECRET --email-cfg=static/fixtures/emailer.json.sample --log-debug=true &`