Add message flag to readme usage section

Author: nnmrts

readme.md

@@ -64,6 +64,7 @@ $ np --help
     --release-draft-only    Only opens a GitHub release draft
     --test-script           Name of npm run script to run tests before publishing (default: test)
     --no-2fa                Don't enable 2FA on new packages (not recommended)
+	--message               Version bump commit message, '%s' will be replaced with version (default: version)
 
   Examples
     $ np
@@ -98,6 +99,7 @@ Currently, these are the flags you can configure:
 - `releaseDraft` - Open a GitHub release draft after releasing (`true` by default).
 - `testScript` - Name of npm run script to run tests before publishing (`test` by default).
 - `2fa` - Enable 2FA on new packages (`true` by default) (setting this to `false` is not recommended).
+- `message` - The commit message used for the version bump. Any `%s` in the string will be replaced with the new version (`%s` when using npm and `v%s` when using yarn by default)
 
 For example, this configures `np` to never use Yarn and to use `dist` as the subdirectory to publish: