Update "What's New in CTSM 5.3"

[samsrabin]

Description of changes

• Rearranging a bit to highlight things that users probably care about more than software engineers.
• Removing line breaks, as this harms searchability.
• Using hash marks as Markdown headers instead of title underlines, as these are easier to understand.

It might be easier for further discussion to take place in a Google Doc for now... I've made one here.

Specific notes

Contributors other than yourself, if any: @ekluzek

CTSM Issues Fixed: None

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

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

Does this create a need to change or add documentation? Did you do so? No

Testing performed, if any: None needed.

Remaining questions/tasks

• Add links to PRs/issue throughout, so that users can get more information. (will do in Google doc)
• Move to docs directory? (leave for now)

[ekluzek]

This is great. Love the cleanup here.

[ekluzek]

@samsrabin it would be nice to bring this in, should maybe you and I meet to go over it?

[ekluzek]

I'd like to see this come in, but what should happen is we finish the notes in the Google Doc and have that be what comes in.

[ekluzek]

I'm going to resolve conversations and just merge this to b4b-dev so it's in place. It has important improvements already. We'll bring more in with the full document, but good to bring in this part.