Adjust package name to PyPI practice

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

README.md

@@ -16,7 +16,7 @@ This repository can be installed from PyPI or from source.
 ### Installing from PyPI
 
 ```bash
-pip install case_utils
+pip install case-utils
 ```
 
 Users who wish to install from PyPI should be aware that while CASE's ontology is in its pre-1.0.0 release state, backwards-incompatible ontology changes may occur.  This may manifest as [`case_validate`](#case_validate) reporting data review errors after installing an updated `case_utils` version.  Users may wish to pin `case_utils` within any dependent code bases to be less than the next unreleased SEMVER-minor version.  (E.g. if `case_utils` version `0.8.0` is currently available, a newly adopting project might wish to track `case_utils<0.9.0` among its dependencies.)