This information is for people who are working on the development of TiddlyWiki5 itself, and isn't relevant for end users
Installing TiddlyWiki5 with NPM downloads a snapshot release of TiddlyWiki5. To use a development copy of the TiddlyWiki5 repository instead of the copy installed by NPM, use this command within the root of the TiddlyWiki5 repo:
npm link
As releases are made during development it is necessary to adjust the version number of the TiddlyWiki5 core. This is done with the npm version command. For example:
npm version 5.0.0-alpha.10
As described in #10 in this article by npm's author, when run from within a git repo this command will also commit the change and tag it