Update getting-started.md (#1343)

Update getting-started.md (#1343)

* Update getting-started.md

Lines 12 - 15.

More clarity on how to add PATH entry for Alire ecosystem client installed on a user's local Linux machine.
PATH value was missing the required double quotes.

* Update getting-started.md

To offer users a choice of adding the Alire client environment to their PATH environment either just for their current terminal session or for future sessions also.

* Update getting-started.md

Put PATH entries into .profile rather than .bashrc since some users may not be using the bash shell, i.e. may be using csh, zsh, fsh, etc.