Add license (Apache 2.0)

[romanc]

Description

Add license as found missing in issue #85.

Fixes #85

How Has This Been Tested?

No tests have been done.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation: N/A
• My changes generate no new warnings: N/A
• Any dependent changes have been merged and published in downstream modules: N/A
• New check tests, if applicable, are included: N/A

[romanc]

Unrelated, but we require 3.11, so I though I'd change it along the way

[FlorianDeconinck]

@bensonr We are clear for this, correct?

[bensonr]

@FlorianDeconinck - I thought an earlier PR had taken care of licensing, but see it had not. Regardless, this is a derivative work and the license will be kept the same. I am checking as to who now owns the copyright.

[romanc]

Frank added the Apache License to PyFV3 in NOAA-GFDL/PyFV3#31 if that is what you were having in mind.

[fmalatino]

lgtm

[FlorianDeconinck]

Hold for Rusty's green light. Ok with me.