statement of need in package documentation

[corybrunson]

JOSS expects the package documentation itself to include a statement of need. Based on previous conversations, this need not be a full section as in the manuscript but could be a sentence or two in Getting Started. Maybe it's already there in another section; if so, please point me to it and accept my apology!

Part of this JOSS review.

[yemeen]

expanded the introduction statement to better explain the scope of the package and target audience!

[corybrunson]

Thanks! It's in this new branch, right? Once merged into JOSS-Paper, i'll close the issue.