docs(readme.md): fix installation command (#3)

Steven Petryk · web-flow · commit 9d4c46d9ccb4 · 2019-08-01T15:15:46.000-07:00
diff --git a/README.md b/README.md
@@ -14,7 +14,7 @@ ensure that breaking changes to our Content Types don't cause an outage, and bec
 ## Usage
 
 ```sh
-yarn install --dev contentful-typescript-codegen
+yarn add --dev contentful-typescript-codegen
 ```
 
 Then, add the following to your `package.json`:
