Create the API authentication documentation

The api-authentication.md file is based on the online version at:
https://docs.cachethq.io/docs/api-authentication

docs/api/api-authentication.md

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+# API Authentication
+
+Authenticating your protected API requests.
+
+Cachet is built on the belief that your service status is open and transparent,
+therefore all `GET` requests are public and require no authentication to access
+the information. The following are exempt from this rule:
+
+- Disabled components will only return in the Component API if you provide a
+  valid API token.
+- The Subscribers API will only work if you provide a valid API token, we
+  don't want to expose email addresses.
+
+All other requests require authentication, either with `Basic Auth` or the
+preferred `API Token`.
+
+## Basic Auth
+
+When making any request to the API which is not a `GET`, you'll need to use
+some kind of authentication. The simplest of the authorization methods offered
+by Cachet is [BasicAuth][1].
+
+> **This is not secure**  
+> For obvious reasons, sending your authentication details in plain text is not
+> secure. We do advise that you add SSL to your Cachet installation for added
+> security, but suggest using API tokens.
+
+To authenticate your requests you only need to provide your email and password.
+
+```
+$ curl -u username@example.com:password -H "Content-Type: application/json" \
+  -d '{"name":"API","description":"An example description","status":1}' \
+  http://status.cachethq.io/api/v1/components
+```
+
+## API Token
+
+The API Token is generated at installation time for the main user or when a
+new team member is added to your status page and can be found on your profile
+page (click your profile picture to get there).
+
+Once you have your token you'll need to add a new request header of
+`X-Cachet-Token: TOKEN`
+
+```
+$ curl -H "Content-Type: application/json;" -H "X-Cachet-Token: YOUR_KEY_HERE" \
+  -d '{"name":"API","description":"An example description","status":1}' \
+  http://status.cachethq.io/api/v1/components
+```
+
+
+
+[1]: http://en.wikipedia.org/wiki/Basic_access_authentication
+
+