Overview
VHDL-Tool makes its services available to Atom through the Language Server Protocol.
Atom plugin
$ git clone https://git.vhdltool.com/vhdl-tool/vhdltool-atom
$ cd vhdltool-atom
$ apm install
$ apm install language-vhdl
$ apm install nuclide
Then launch Atom from the root of your design, where the configuration file is located:
$ atom .
Troubleshooting
Make sure vhdl-tool is configured properly by running vhdl-tool check-config in the directory containing the configuration file.