Describe difference between just "recipe" and playbook tags on docs/installing.md

[luixxiul]

Is your feature request related to a problem? Please describe.
Context: #3739

The documentation file docs/installing.md should describe difference between just "recipe" and the playbook tags, as for most of people who have never heard of just, it is almost impossible to see the difference between just install-all and just run-tags install-all without knowing what just is, let alone the documentation itself explains what to be done by using just commands here, which compounds the confusion.

Describe the solution you'd like
See above.

Describe alternatives you've considered

Additional context
Of course it should be clear how just works for those who know what just is, but it does mean that most people know what just is. As documentation to explain installing, it should be one of the most important articles and therefore the confusing description should be avoided as much as possible.