Since Atom is still not very stable yet, it might crash due to the windows in open during startup. One quick life-saving trick is to run the program from command line by atom --clear-window-state.
To install or update Atom packages, go to Packages > Settings View > Manage Packages.
linter-languagetool. The free LanguageTool has to be installed locally with the multiple-GB N Gram Data package installed on the computer as well. Then in the settings of the package, provide the paths for the installed languagetool-server.jar and the N Gram Data.markdown-preview-plus plugin. Pandoc has to be installed on the computer. On the settings of the plugin package, Pandoc options was set to --filter=pandoc-eqnos in my case for rendering MathML equations for this website code. The keybinding ctrl+shift+M should toggle the preview window while ctrl+shift+X should run the render.