Binder link targets 2022 fork of bashcrawl

The README.md link to Binder targets the fork of bashcrawl in which the feature was developed. This is starting to show its age. Either @nthiery needs to git pull or (proper fix) the binder must be repointed to the official remote.

My current workaround:

set +x +e
git remote add upstream https://gitlab.com/slackermedia/bashcrawl.git
git checkout -b up upstream/master
. ~/.binder/postBuild