Revert ".gitignore: Add config.yml"

This reverts commit bddab8d152e6cb79fdd15fd237f63eb54c0789ac.
README*: Update documentation
.gitignore: Add config.yml
config.yml -> config_example.yml
src/cljs/choices/core.cljs: Remove println leftover
src/cljs/choices/core.cljs: Compute max value for a score

Don't set the max value for a score manually: compute it from the
sum of possible positive increments of the value when the user go
through the choices.
src/cljs/choices/core.cljs: Fix bug
Allow to display scores in the final message as percentage

Score variables can now have a "max" value used to express the final
score value as a percentage.
Implement format strings for scores in the score final message
config.yml: Fix progress bar setup
Fix copyright headers
src/cljs/choices/core.cljs: Small syntactic fix
resources/public/css/choices.css: Update Bulma to 0.9.4
deps.edn: Bump reagent/reagent version

Also add cljsjs/react and cljsjs/react-dom as this is now required
since reagent 1.1.0.

See https://github.com/reagent-project/reagent/blob/master/CHANGELOG.md#110-2021-06-05
deps.edn: Bump some dependencies
.gitignore: Ignore more directories
README*: Small enhancements
deps.edn: Bump dependencies
Update the "Contribute" section
README.md: New file