Add gulp-rev-sri to readme (#260)

Author: shaunwarman

readme.md

@@ -206,3 +206,4 @@ It may be useful - and necessary - to use `gulp-rev` with other packages to comp
 - [gulp-rev-delete-original](https://github.com/nib-health-funds/gulp-rev-delete-original) - Delete original files after rev
 - [gulp-rev-loader](https://github.com/adjavaherian/gulp-rev-loader) - Use rev-manifest with webpack
 - [gulp-rev-format](https://github.com/atamas101/gulp-rev-format) - Provide hash formatting options for static assets (prefix, suffix, last-extension)
+- [gulp-rev-sri](https://github.com/shaunwarman/gulp-rev-sri) - Add subresource integrity field to rev-manifest