add link to netlify cli

Author: bahmutov

.gitignore

@@ -1 +1,3 @@
 node_modules/
+cypress/videos
+cypress/screenshots

CONTRIBUTING.md

@@ -3,3 +3,10 @@ How to [code a plugin](https://github.com/netlify/build/blob/master/docs/creatin
 ## Testing and releasing a new version
 
 Try using `beta` branch to release new pre-release versions of the plugin by following [the semantic release guide](https://github.com/semantic-release/semantic-release/blob/master/docs/recipes/pre-releases.md). You can fork and test out new versions published to NPM using the [netlify-plugin-cypress-example](https://github.com/cypress-io/netlify-plugin-cypress-example) repository. Hope the `master` branch merged into `beta` does not bring features and fixes *already released*. Thus I suggest using `beta` branch for new features.
+
+If helps to install [Netlify CLI](https://github.com/netlify/cli) to test the plugin locally
+
+```shell
+npm install netlify-cli -g
+netlify build
+```