Add NSM mention in desktop file

[Houston4444]

Hi @theGreatWhiteShark .

add NSM mention to the desktop file allows it to be listed by NSM session managers. See jackaudio/new-session-manager#40 .

Now in RaySession, it prevents to need to check version with hydrogen --version.

I don't know if it is possible to build hydrogen without liblo, if it is the case, this key 'X-NSM-Capable' should be set on true or false conditionally.

[theGreatWhiteShark]

Hey @Houston4444 ,

You set the master branch of your fork as target of this PR. Is this intended?

Sounds good to me. But I have to admit that I don't know much about XDG. Hydrogen itself is not XDG-compatible yet (see hydrogen-music#643). I'm not quite sure whether this might affect the changes you applied.

[Houston4444]

You set the master branch of your fork as target of this PR. Is this intended?

Oh, its a mistake (directly made in github), but not strong, I removed my fork and re-fork before the PR.

Hydrogen itself is not XDG-compatible yet

This key is XDG-compatible, If I have the key in the desktop file, it is ok for me, I don't care about the rest of XDG. The .desktop file is already installed at the good place ;).

[theGreatWhiteShark]

The .desktop file is already installed at the good place

Great.

Could you make a PR containing these changes against the master branch of hydrogen?

[Houston4444]

Heeee ! I haven't seen I was making a PR on my own fork !!! ;)