Option 1: use the atom package manager (apm)
From the command line:
apm install <github repo link>
Where the github link is the same link you'd normally use to clone the repository.
apm install
documentation
$ apm help install
Usage: apm install [<package_name>...]
apm install <package_name>@<package_version>
apm install <git_remote>
apm install <github_username>/<github_project>
apm install --packages-file my-packages.txt
apm i (with any of the previous argument usage)
Install the given Atom package to ~/.atom/packages/<package_name>.
If no package name is given then all the dependencies in the package.json
file are installed to the node_modules folder in the current working
directory.
A packages file can be specified that is a newline separated list of
package names to install with optional versions using the
`package-name@version` syntax.
Options:
--check Check that native build tools are installed [boolean]
--verbose Show verbose debug information [boolean] [default: false]
--packages-file A text file containing the packages to install [string]
--production Do not install dev dependencies [boolean]
-c, --compatible Only install packages/themes compatible with this Atom version [string]
-h, --help Print this usage message
-s, --silent Set the npm log level to silent [boolean]
-q, --quiet Set the npm log level to warn [boolean]
Prefix an option with `no-` to set it to false such as --no-color to disable
colored output.
Option 2: Download manually
The following seemed to work for me on MacOS
cd ~/.atom/packages
git clone https://github.com/url_to_your_package
cd your_package
apm install