Update README.md

[mrbeandev]

I ran into this error, a widespread error we get when we install a project. So it is good to mention this in the readme so users don't have to search the web for hours like I did

[mcmonkey4eva]

We don't generally list every possible mistake & solution in README's, this one here is a basic YAML formatting mistake, it's better to make simple issue/discussion posts with clear titles & examples so if someone else has the same issue they will find it quickly with a google search.
Or alternately build a FAQ/Troubleshooting guide, but that should be done by someone with more experience so they can make sure the solutions are all correct and relevant