If you want to contribute to TiddlyWiki's development, rather than installing TiddlyWiki in the usual way, you can work directly with the GitHub repository.
Mario Pietsch has created a short video introduction.
npm link
(Windows) or sudo npm link
(Mac/Linux) to tell npm to use this copy of the repo as the globally installed oneAfter this procedure you can work with TiddlyWiki5 via npm as though it were installed in the usual way with npm install -g tiddlywiki
.
See also Scripts for TiddlyWiki on Node.js.