03-packaging-installing: provide further explanation of `.` in `pip install .`

[tobyhodges]

During the pilot lesson at CC@Home2020, learners were unclear on the meaning of . in the pip install . command. The material could be improved by expanding on this to make the use of a relative path explicit.

[vinisalazar]

Relative to this issue: I believe that the "Pip" section is a bit out of place in this Episode. There is no need to mention Pip until after the example package has been created.

I would suggest moving it right after the "SetupTools and installing locally", right after the first pip install -e ., and make use of that command as a "hook" to start talking about Pip.