Add a plugin tutorial to the README

README.md

@@ -1 +1,65 @@
 # airshipctl
+
+### Custom Plugins Tutorial
+
+The following steps will get you started with a very rudimentary example plugin
+for airshipctl. First, create a directory for your project outside of the
+GOPATH:
+```
+mkdir /tmp/example
+cd /tmp/example
+```
+This project will need to be a go module. You can initialize a module named
+`example` with the following:
+```
+go mod init example
+```
+Note that modules are a relatively new feature added to Go, so you'll need to
+be running Go1.11 or greater. Also note that most modules will follow a naming
+schema that matches the remote version control system. A more realistice module
+name might look something like `github.com/ian-howell/exampleplugin`.
+
+Next, create a file `main.go` and populate it with the following:
+```go
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/ian-howell/airshipctl/cmd"
+	"github.com/spf13/cobra"
+)
+
+func main() {
+	rootCmd, err := cmd.NewRootCmd(os.Stdout)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to create root airshipctl command: %s\n", err.Error())
+		os.Exit(1)
+	}
+
+	exampleCmd := &cobra.Command{
+		Use:   "example",
+		Short: "an example plugin",
+		Run: func(cmd *cobra.Command, args []string) {
+			fmt.Fprintln(os.Stdout, "Hello airshipctl!")
+		},
+	}
+
+	rootCmd.AddCommand(exampleCmd)
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Fprintf(os.Stderr, "Failure during execution: %s\n", err.Error())
+		os.Exit(1)
+	}
+}
+```
+And finally, run the build command to download and compile `airshipctl`:
+```
+go build -o airshipctl
+```
+Now that you've built `airshipctl`, you can access your plugin with the following command:
+```
+./airshipctl example
+```
+
+For a slightly more involved example, see the [example plugin project](github.com/ian-howell/examplepugin)