Improve instructions for making the axii command globally available

The documentation currently states that following the suggested instructions (= agreeing to the settings suggested by the installer?) led to the axii command being globally available afterwards. However, the default value is no/N, when asking the user whether to add axii to the .bashrc/.[...]rc.

Furthermore, it ensures that a reader of the documentation is aware of the requirement to re-open the terminal or to perform a re-source, before being able to use the axii command as advertised.