Go to 'Tools -> Options -> Game profiles' and create a new game configuration by copying your HL or HLDM configuration. Then:
- Game tab: remove any .fgd files and add
dmc.fgd instead (this file is included in the FGD collection here).
- Directories tab: I think you only need to change the 'Mod Directory' to point at your Half-Life\dmc folder.
- Textures tab: any .wad files you're using must either be part of DMC, or you'll have to distribute them alongside your map (you can embed textures into maps to make things easier for players). It's easier to only select DMC wad files for now.
- Build Programs tab: you can use the same compile tools as for HL/HLDM, so no changes required here.
Finally, if you want to run your maps from the editor, go to the 'Run map' menu (by pressing F9 when a map is open) and make sure that the game is launched with the
parameter. In normal mode, that goes in the 'Additional game parameters' input. In expert/advanced mode, it goes in the 'Parameters' input of the game_exe command (which is typically located at the bottom).
I don't have DMC here to verify so I might be wrong on some of the details. Let us know if this works for you.