Add commas to sentence in using_tilemaps.rst

[Lukas-Fletcher]

Will conflict with #9870. Could be changed to parentheses instead of commas.
I got confused when reading the sentence because "the layers you aren't currently editing from" all flow together but then what's left of sentence doesn't make sense "the same TileMap node will appear grayed out while in the TileMap editor". Hope the extra commas will help with the flow.
Another solution would be to rephrase it as "In the 2D editor, the layers from the same TileMap node that you aren't currently editing will appear grayed out while in the TileMap editor." or something along those lines.

[Geometror]

What about "In the 2D editor, the layers of a TileMap node you aren't currently editing will appear grayed out." ?
I've checked the behavior and the last part ("... in the TileMap editor") isn't actually the case (or I'm misunderstanding) so I think it can be removed, which makes the sentence even clearer.

[Lukas-Fletcher]

@Geometror After some testing my understanding is also that it isn't actually the case. I agree that part probably should be removed. I don't know at what stage the transitioning from TileMap to TileMapLayer in the documentation is in but "In the 2D editor, the TileMapLayer nodes you aren't currently editing will appear grayed out." might be more fitting.

[skyace65]

This needs to be updated since #9870 was merged