Documentation: Explain use of message categories, especially info vs neutral

[NetSysFire]

Describe the bug

There is no documentation on how message categories in p->add_msg_if_player() should be used.

Steps To Reproduce

n/a

Expected behavior

Most are self-explanatory but it would be great if they could still be explained somewhere. In particular I found it hard to distinguish between m_info and m_neutral and I think there should be some official guidance about that somewhere.

Screenshots

No response

Versions and configuration

n/a

Additional context

No response

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not 'bump' or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not bump or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[GuardianDll]

https://github.com/CleverRaven/Cataclysm-DDA/blob/master/doc/EFFECT_ON_CONDITION.md#u_messagenpc_message

explain it from the EoC perspective in "type"

https://github.com/CleverRaven/Cataclysm-DDA/blob/master/src/enums.h#L346-L364

explain it in enums.h

https://github.com/CleverRaven/Cataclysm-DDA/blob/master/src/output.cpp#L3090-L3101

explain each color it may have

Where this info should be documented?

[NetSysFire]

Ideally in our Manual of Style