Update README: Sandbox -> Virtual Environmen (#407)

* Update README: Sandbox -> Virtual Environment

* rm changelog entry

Author: bbkane

README.md

@@ -136,7 +136,7 @@ pipx install git+https://github.com/psf/black.git@ce14fa8b497bae2b50ec48b3bd7022
 pipx install https://github.com/psf/black/archive/18.9b0.zip  # install a release
 ```
 
-### Walkthrough: Running an Application in a Temporary, Sandboxed Environment
+### Walkthrough: Running an Application in a Temporary Virtual Environment
 
 This is an alternative to `pipx install`.