[Feature]: Add Makefile

[forsyth2]

How will this affect the next version number?

New feature (increment MINOR version)

Is your feature request related to a problem?

Yes, #30. /build doesn't always get deleted.

Describe the solution you'd like

Add makefile similar to https://github.com/E3SM-Project/e3sm_diags/blob/821c84e108f01a3d6c0951ba8cf4018ecb06231b/Makefile#L100-L101

Describe alternatives you've considered

No response

Additional context

No response

[forsyth2]

Alternatively, or perhaps in tandem with, consider use of git worktree (from https://git-scm.com/docs/git-worktree: "A git repository can support multiple working trees, allowing you to check out more than one branch at a time.")