doc that masterlist actflag is just h0 in practice, doc that masterlist has all the fields.

[johnpaulalex]

Description of changes

document that masterlist actflag is just h0 in practice, document that masterlist has all the fields.

Specific notes

Contributors other than yourself, if any: none

CTSM Issues Fixed (include github issue #): none

Are answers expected to change (and if so in what way)? no

Any User Interface Changes (namelist or namelist defaults changes)? no

Testing performed, if any: none

[samsrabin]

Just a heads up: I expect this to have conflicts with #2087, which is due to be brought in soon. They shouldn't be too hard to resolve, though.

[ekluzek]

I looked at the conflicts and there's only one with #2087 and it should be easy to resolve.