add Poetry info

README.md

 # nshmp-lib
+
+## NetCDF Database
+
+## Prerequisites
+
+* [Python](https://www.python.org/downloads/) 3.6+
+* [Poetry](https://python-poetry.org/) Python dependency manager
+
+### Poetry Install
+
+See [Poetry installation](https://python-poetry.org/docs/) instructions for more.