website/docs: document vagrant login

website/docs/source/layouts/layout.erb

@@ -110,6 +110,7 @@
 									<li<%= sidebar_current("cli-destroy") %>><a href="/v2/cli/destroy.html">destroy</a></li>
 									<li<%= sidebar_current("cli-halt") %>><a href="/v2/cli/halt.html">halt</a></li>
 									<li<%= sidebar_current("cli-init") %>><a href="/v2/cli/init.html">init</a></li>
+									<li<%= sidebar_current("cli-login") %>><a href="/v2/cli/login.html">login</a></li>
 									<li<%= sidebar_current("cli-package") %>><a href="/v2/cli/package.html">package</a></li>
 									<li<%= sidebar_current("cli-plugin") %>><a href="/v2/cli/plugin.html">plugin</a></li>
 									<li<%= sidebar_current("cli-provision") %>><a href="/v2/cli/provision.html">provision</a></li>

website/docs/source/v2/cli/login.html.md

@@ -0,0 +1,30 @@
+---
+page_title: "vagrant login - Command-Line Interface"
+sidebar_current: "cli-login"
+---
+
+# Login
+
+**Command: `vagrant login`**
+
+The login command is used to authenticate with a
+[Vagrant Cloud](http://www.vagrantcloud.com) server. Logging is only
+necessary if you're accessing protected boxes or using
+[Vagrant Share](/v2/share/index.html).
+
+**Logging in is not a requirement to use Vagrant.** The vast majority
+of Vagrant does _not_ require a login. Only certain features such as protected
+boxes or [Vagrant Share](/v2/share/index.html) require a login.
+
+The reference of available command-line flags to this command
+is available below.
+
+## Options
+
+* `--check` - This will check if you're logged in. In addition to outputting
+  whether you're logged in or not, the command will have exit status 0 if you're
+  logged in, and exit status 1 if you're not.
+
+* `--logout` - This will log you out if you're logged in. If you're already
+  logged out, this command will do nothing. It is not an error to call this
+  command if you're already logged out.