Update documentation for Work Queue perl module, which is no longer shipped with Conda

[amaltaro]

After following the recommended cctools installation steps through conda, I started testing my setup with the instructions provided in this section:
https://cctools.readthedocs.io/en/stable/install/#testing-your-installation

and it turns out that one of the steps fail with something like:

$ perl -MWork_Queue -e 'print("$Work_Queue::WORK_QUEUE_DEFAULT_PORT\n")'                                                                                                                            
Can't locate Work_Queue.pm in @INC (you may need to install the Work_Queue module) (@INC contains: /Library/Perl/5.34/darwin-thread-multi-2level ... etc

After talking to Ben, he confirms that Work Queue perl module is no longer shipped with the conda package.

Hence, the documentation needs to be updated accordingly. So far, at least the section above has been identified.