Adding a '--no-add' option

[phil-blain]

Hi @jakub-g !

Thanks for this script, it's very useful for resolving simple conflicts. I was wondering if you would be willing to accept a PR to add an optional option --no-add to prevent the script from running git add ?

I often want to check the files with git diff before adding them. This would not change the default behaviour of the script.

[phil-blain]

base...phil-blain:git-resolve-conflict:no-add