DOC: tutorial improvements

[fletchapin]

• I have reviewed the documentation on main here.

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Location of Documentation

https://we3lab.github.io/pype-schema/hello.html

Documentation Problem

The "hello world" tutorial is too vague and could be improved with more detail.

Suggested Fix

• Expand the intro text “A class hierarchy designed to represent configurations of process engineering systems, such as wastewater treatment or desalination plants” to explain the value and/or compare to other existing tools. E.g. “this tool allows for process flow representations within a specific facility. The structure of the network representation for a facility is analogous to the representation for larger water network representations, such as those in EPAnet or SWMM”. Needs more wordsmithing but in general just explaining more what PyPES does
• Include some description of how to actually assign data values to a tag? Maybe I’m missing this but I wasn’t finding it.

[fletchapin]

In addition, @LilyLiu0719 mentioned that num_units is not well documented in JSON Representation and an example use case would be helpful