The easiest method is to Ctrl-Shift-P in VSCodium, select "Extensions: Install from VSIX", and point it at the azcobu.main-sequence-0.0.1-universal.vsix file in the repo root.

Alternately, you can install it manually:

1. Find the extensions folder for VSCode:
   • Linux: ~/.vscode/extensions - for VSCodium it's ~/.vscode-oss/extensions
   • Windows: %USERPROFILE%\.vscode\extensions
   • macOS: ~/.vscode/extensions
2. Copy the folder 'azcobu.main-sequence-0.0.1-universal' and its contents into it.
3. Restart VSC, and go to File > Preferences > Theme > Color Theme, click, and select Main Sequence from the list.