Create TechTips with short vidoes for sources and sinks

[ACowan0105]

Idea is to create small models (called "TechTips" that demonstrate various features and shortcuts for how to use VCell. These should be accompanied by short pdfs and videos associated and posted on both website and youtube. This first one explains how to create sources and sinks with vcell reactions.

Process is:

Build Model as user "vcelluser" with name (TechTip: Useful Name); use text annotations to explain what the model demonstrates. Make this model Public and Dan will assign a new category of models labeled as "TechTip"

Write up Short pdf (or perhaps have a page on the website with individual Tech Tips written out to link directly to, bypassing pdf.

Make short video eplaining in words what the model shows. Add to Youtube channel.

[ACowan0105]

Replaces VCell development issue 197