Git(Hub) newbie... Added support for M5StackCore (vs Core2) with a little renaming... Help in commit / merging back etc.

[SeanPGit]

So - the time has come... I'm a complete GitHub newbie (ageing dinosaur of old - last used Perforce for source control!).

I've made my first "contribution" in my own fork, but sitting here on my PC; I think could be worthy of a merge back to main, but I I also want to "re-sync" back to the latest commits from the main fork...

I've added support for:

1. "M5Stack Core (Basic)" vs the existing M5 Stack Core support which is actually "Core 2" (so a little renaming of the platform.io entries).
2. A small change to reporting Wifi details in "Wifi Not Enabled" (in build!) as that confused me a little.
3. Buttons supported to switch effects & info screen on this and M5 Stick builds.
4. One change - adding more effects to "my" DEMO build because I wanted to see them on my platforms (to cycle through!).

I've:

• Forked the main project to my own repository. https://github.com/SeanPGit/NightDriverStrip
• Updated the relevant files (on my PC), and understand first need to commit back to my fork,,,
• I ALSO want to re-sync back to main project (but keeping "some" changes in other files not related to "this" change!)
• Tested my build on my platform (and M5-Stick C+; was "unaffected").
• Not done a full "buddy build" or equivalent as it'd take literally a day++ on my platform!
• There is a re-boot crash on the M5 Stack Core that I need to look into! (I think related to lack of, or mis-specified RAM for the platform!)
• There's one file I don't want to commit changes to (effects.cpp) because I included more effects to test it with DEMO (could ALSO be the reason for the reboots).

I'd like to understand the series of actions I need to make to "commit" to my fork, but supress effects.cpp from that?
Then submit for approval back to main project...
Then re-sync back to main project...
(Can one "re-sync and merge back" to my own Fork or that on my PC?)