pre-merge issue with `rm -rf node_modules`

I like the idea of #35 a lot, but it caused me a problem. For `pre-merge` I want to remove all npm packages with `rm -rf node_modules`, and then reinstall them. But, then pre-git changes the `package.json` file again on reinstall, changing my settings in `package.json` (for instance, adding the commit script, which I don't want) and recreating the git hooks. I solved this by doing `npm prune`, `npm update` instead, which is probably better anyway… I think. It might be better to use this approach in the README.

Read the README section describing pre-merge and the behavior around reinstalling packages. Reproduce the reported flow with npm prune and npm update, then document the approach that avoids unwanted package.json changes and recreated hooks. Done means the README clearly explains the safer commands and their effect.

Written by the indexing model from the issue text.