Expand `Equipment` mention in `README`

[CBroz1]

The usage section of the README should be expanded to more closely parallel the corresponding section in element-array-ephys, inclusive of more specificity about upstream tables. The README should discuss where an Equipment table should be declared, and point to the declaration in the example workflow, as discussed in DataJoint Elements issue #39.

[CBroz1]

I generated a more expansive Diagram that specifies lab.Equipment, but I'm not familiar with how to add lines to designate upstream/downstream. Linked files: DOT and SVG.

[kabilar]

Thanks @CBroz1. The dashed lines to designate upstream and downstream tables are added manually with any image processing tool that one is comfortable with (e.g. draw.io).