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

docs/content/doc/development/cli.md

@@ -0,0 +1,34 @@
+---
+date: "2019-03-31:00:00+01:00"
+title: "Adding new cli commands"
+draft: false
+type: "doc"
+menu:
+  sidebar:
+    parent: "development"
+---
+
+# Adding new cli commands
+
+All cli-related functions are located in `pkg/cmd`.
+Each cli command usually calls a function in another package.
+For example, the `vikunja migrate` command calls `migration.Migrate()`. 
+
+Vikunja uses the amazing [cobra](https://github.com/spf13/cobra) library for its cli.
+Please refer to its documentation for informations about how to use flags etc.
+
+To add a new cli command, add something like the following:
+
+{{< highlight golang >}}
+func init() {
+	rootCmd.AddCommand(myCmd)
+}
+
+var myCmd = &cobra.Command{
+	Use:   "My-command",
+	Short: "A short description about your command.",
+	Run: func(cmd *cobra.Command, args []string) {
+		// Call other functions
+	},
+}
+{{</ highlight >}}

docs/content/doc/development/migrations.md

@@ -25,9 +25,9 @@ and a more in-depth description of what the migration actually does.
 
 To easily get a new id, run the following on any unix system: 
 
-```bash
+{{< highlight bash >}}
 date +%Y%m%d%H%M%S
-```
+{{< /highlight >}}
 
 New migrations should be added via the `init()` function to the `migrations` variable.
 All migrations are sorted before being executed, since `init()` does not guarantee the order.
@@ -37,7 +37,7 @@ to ensure it will be created on new installations.
 
 ### Example
 
-```go
+{{< highlight golang >}}
 package migration
 
 import (
@@ -66,6 +66,6 @@ func init() {
 		},
 	})
 }
-```
+{{< /highlight >}}
 
 You should always copy the changed parts of the struct you're changing when adding migraitons.

docs/content/doc/development/structure.md

@@ -51,6 +51,14 @@ This is where most of the magic happens. Most packages with actual code are loca
 
 This folder holds a simple caldav implementation which is responsible for returning the caldav feature.
 
+### cmd
+
+This package contains all cli-related files and functions.
+
+To learn more about how to add a new command, see [the cli docs]({{< ref "cli.md">}}).
+
+To learn more about how to use this cli, see [the cli usage docs]({{< ref "../usage/cli.md">}}).
+
 ### config
 
 This package configures the config. It sets default values and sets up viper and tells it where to look for config files,