By convention, code markup (`~`) is reserved for keybindings in Org-based
documentation in Spacemacs. Verbatim markup (`=`) is reserved for code and
other code-like things. So change several readmes to reflect this convention.
Use verbatim markup for things like (non-exhaustive list):
- Emacs Lisp functions, modes, buffers, etc.
- Environment variables
- Directory paths
- Code in general