update README

Author: Alban Bailly

README.md

@@ -12,13 +12,19 @@ you may need to install the Gatsby CLI as well `npm install -g gatsby-cli`
 
 Check out the site at http://localhost:8000/
 
+If you'd like to use a local YAML file to build the API docs, run:
+
+`yarn develop [relative-path-to-your-local-YAML-file]`
+
+ex: `yarn develop ../linode-api-docs/openapi.yaml`
+
 ### Build
 
 The API documentation in this site is also indexed in Algolia, so that
 it can be searched across Linode's services. The scripts for this are
 located in the `/search` directory. In order to run them correctly,
-you will need to create a `.env` file in the root directory with the 
+you will need to create a `.env` file in the root directory with the
 following values:
 
 ALGOLIA_API_KEY=(your key here)
-ALGOLIA_API_SECRET=(your secret here)
+ALGOLIA_API_SECRET=(your secret here)