Add changelog for 6.5

[maxrjones]

Description of proposed changes

Starting the 6.5 changelog

Fixes #

Reminders

• Make sure that your code follows our style. Use the other functions/files as a basis.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Describe changes to function behavior and arguments in a comment below the function declaration.
• If adding new functionality, add a detailed description to the documentation and/or an example.

[maxrjones]

@PaulWessel @joa-quim I'm sorry for causing a delay in the release, but I am swamped with AGU prep today and will need to revisit this over the weekend. If anyone wants to take it over to get it out earlier, please feel welcome.

[PaulWessel]

No worries. I will see what we can do.

[maxrjones]

I think this is ready to go if someone @PaulWessel or @Esteban82 is able to provide a review

[PaulWessel]

Looks great, thanks Max.