added windows 7zip workaround in readme (#240)

Author: fernando-cortez

README.md

@@ -20,6 +20,8 @@ Platforms : Windows, Mac
 ## Getting the project
  - A release version can be downloaded from the [Releases](https://github.com/Unity-Technologies/com.unity.multiplayer.samples.coop/releases) page. 
  - Alternatively: click the green `Code` button and then choose to download the zip archive. Remember, that you would download the branch that you are currently viewing in Github.
+ - For Windows users: Using Windows' built-in extracting tool may generate a "Error 0x80010135: Path too long" error window which can invalidate the extraction process. A workaround for this is to shorten the zip file to a single character (eg. "c.zip") and move it to the shortest path on your computer (most often right at C:\\) and retry. If that solution fails, another workaround is to extract the downloaded zip file using 7zip.
+
 
 ## Installing Git LFS