Added pre-rendering note to README.md

Author: NJalal7

README.md

@@ -17,3 +17,6 @@ yarn test
 ```
 
 For detailed explanation on how things work, checkout the [CLI Readme](https://github.com/developit/preact-cli/blob/master/README.md).
+
+Note: When pre-rendering, your module as components are executed in a Node.js environment, where most Web APIs are not available. To account for this, wrap that code in a check like `if (typeof window !== 'undefined')`. 
+Do not add `preact build --no-prerender` to the build command as it will prevent blog posts from rendering.