One of the key issues I keep having at my work, is to keep track which Git commit corresponds with the update at customer premises.

... and now I think "But what if I could add a note (like a note, added at an Excel cell), something like this:

Does such a thing already exists in Git/Git Extensions?

Edit: There already exists a 'notes' feature, but how to use it?
I'd like to thank phd and hlovdal for your very quick response. Apparently there is a "Notes" feature, and I can confirm that my Git installation knows about it, as can be seen from this Git Bash excerpt:

<Git Repository> (master)
$ git notes show
error: no note found for object c1ead08e97978300e4b703eb29d64782b6361062.

=> "Notes" seems to exist, but is it possible to execute a "Notes"-related command without error?

<Git Repository> (master)
$ git notes list

=> Yes, it is possible to execute a "Notes"-related command without error.

<Git Repository> (master)
$ git blabla
git: 'blabla' is not a git command. See 'git --help'.

=> Anyway, if it did not exist, this would have been the result.

... But what about my Git-Extensions application? Well, I don't find it anywhere, so I looked for it in the helpfile:

My menu looks different than that, but there is a shortcut key Ctrl+Shift+N, let's try it.

Bad idea: my Git-Extensions application went into "Not reponding", and even although it takes more than 10 minutes to write down this edit, it still is not responding :-)

For your information: I didn't find "Notes" in the Plugin Manager, so how can I install/activate/use it in my Git-Extensions application?

Edit2: how to go further?
So, it seems that git-notes are indeed pushed onto the Git server, but their visibility depends on the Git client. I am working with Git-Extensions, is this a Git client, supporting git-notes? (I believe so, seen the screenshot of the helpfile, but how does it work exactly? My Git-Extension version is "Git Extensions 5.1.1.17970")
Alexander mentioned another feature: "Git tags". What are the possibilities here?

Edit after Visual Studio update:
I've just updated my Visual Studio environment to v17.13.0. Apparently GIT tags have been chosen as a feature, being covered by Visual Studio/GIT-integration, as you can see in this screenshot from the "What's New?" page: