Update .zshrc and refactor related files as needed

README.md

@@ -1,12 +1,13 @@
 # repo containing configs and scripts to set up a box
 
 ### prerequisites
-- install git if not already installed
-- clone this repo
-- if on macOS, install [homebrew](https://brew.sh/)
+- zsh is installed (scripts are written for zsh)
+- git is installed
 - export the env var `BOX_SETUP_OS` to indicate the operating system
-    - (options defined in `set_env_vars` file)
+    - options defined in `set_env_vars` file
+- if on macOS, install [homebrew](https://brew.sh/)
 
 ### script run
+- git clone this repo
 - from the repo's root directory, run `./setup_this_box`