Add stub for shell

README.md

@@ -77,11 +77,11 @@ func main() {
         log.Fatalf("unable to connect to device %s: %v", opts.Address, err)
     }
     defer dev.Disconnect()
-    stdout, stderr, err := dev.Shell("ls")
+    stdout, stderr, errCode, err := dev.Shell("ls")
     if err != nil {
         log.Fatalf("unable to shell into device %s: %v", opts.Address, err)
     }
-    log.Printf("Stdout: %s\nStderr: %s\n", stdout, stderr)
+    log.Printf("Stdout: %s\nStderr: %s\n, ErrCode: %d", stdout, stderr, errCode)
 }
 ```
 

shell.go

@@ -0,0 +1,15 @@
+package adb
+
+import (
+	"context"
+)
+
+// Shell allows you to run an arbitrary shell command against a device.
+//
+// This function is useful if you need to run an obscure shell command or if
+// you require functionality not provided by the exposed functions here.
+// Instead of using Shell, please consider submitting a PR with the functionality
+// you require.
+func (d Device) Shell(ctx context.Context, command string) (stdout string, stderr string, ErrCode int, err error) {
+	return "", "", 1, nil
+}