Added docker troubleshooting info to README

This adds some troubleshooting information for people that are using docker for their rails instances.

Author: venarius

README.md

@@ -428,6 +428,10 @@ There is a [known issue](https://github.com/tailwindlabs/tailwindcss/issues/1724
 
 Please try uninstalling `watchman` and try running the watch task again.
 
+### The `assets:precompile` command is hanging inside a docker container
+
+Make sure your Dockerfile uses a `WORKDIR`. Otherwise Tailwind will also search all operating system files of that container for class names.
+
 ### Lost keystrokes or hanging when using terminal-based debugging tools (e.g. IRB, Pry, `ruby/debug`...etc.) with the Puma plugin
 
 We've addressed the issue and you can avoid the problem by upgrading `tailwindcss-rails` to [v2.4.1](https://github.com/rails/tailwindcss-rails/releases/tag/v2.4.1) or later versions.