Added docs for cli usage and adding new commands (#68)

docs/content/doc/usage/cli.md

@@ -0,0 +1,84 @@
+---
+date: "2019-03-31:00:00+01:00"
+title: "CLI"
+draft: false
+type: "doc"
+menu:
+  sidebar:
+    parent: "usage"
+---
+
+# Command line interface
+
+You can interact with Vikunja using its `cli` interface. 
+The following commands are available:
+
+* [help](#help)
+* [migrate](#migrate)
+* [version](#version)
+* [web](#web)
+
+If you don't specify a command, the [`web`](#web) command will be executed.
+
+All commands use the same standard [config file]({{< ref "../setup/config.md">}}).
+
+### `help`
+
+Shows more detailed help about any command.
+
+Usage:
+
+{{< highlight bash >}}
+$ vikunja help [command]
+{{< /highlight >}}
+
+### `migrate`
+
+Run all database migrations which didn't already run.
+
+Usage:
+{{< highlight bash >}}
+$ vikunja migrate [flags]
+$ vikunja migrate [command]
+{{< /highlight >}}
+
+#### `migrate list`
+
+Shows a list with all database migrations.
+
+Usage:
+{{< highlight bash >}}
+$ vikunja migrate list
+{{< /highlight >}}
+
+#### `migrate rollback`
+
+Roll migrations back until a certain point.
+
+Usage:
+{{< highlight bash >}}
+$ vikunja migrate rollback [flags]    
+{{< /highlight >}}
+
+Flags:
+* `-n`, `--name` string: The id of the migration you want to roll back until.
+ 
+
+### `version`
+
+Prints the version of Vikunja.
+This is either the semantic version (something like `0.7`) or version + git commit hash.
+
+Usage:
+{{< highlight bash >}}
+$ vikunja version    
+{{< /highlight >}}
+
+### `web`
+
+Starts Vikunja's REST api server.
+
+Usage:
+{{< highlight bash >}}
+$ vikunja web    
+{{< /highlight >}}