chore: update README.md

Author: actions-user

README.md

@@ -86,6 +86,13 @@ module "lambda" {
 <!-- markdownlint-disable -->
 ## Makefile Targets
 ```text
+Available targets:
+
+  help                                Help screen
+  help/all                            Display help for all targets
+  help/short                          This help short screen
+  lint                                Lint terraform code
+
 ```
 <!-- markdownlint-restore -->
 <!-- markdownlint-disable -->