fix: link Heretic, Hexen, Strife and Chex Quest

GZDoom now declares the path of each IWAD, so their files resolve by
path and these ids count as held. Their IWADs sit in the Doom folder,
and no parent led them there: the Doom section is theirs too.

scripts/siterender.py

@@ -1339,6 +1339,11 @@ SYSTEM_PARENTS: dict[str, tuple[str, str]] = {
     # Games, filed with the game whose folder holds their data
     "dinothawr": ("Dinothawr", "Dinothawr"),
     "doom": ("Id Software", "Doom"),
+    # The other games of the Doom engines keep their IWADs in its folder.
+    "heretic": ("Id Software", "Doom"),
+    "hexen": ("Id Software", "Doom"),
+    "strife": ("Id Software", "Doom"),
+    "chex": ("Id Software", "Doom"),
     "ctf": ("Id Software", "Quake II"),
     "teamarena": ("Id Software", "Quake III Arena"),
     "enemyterritory": ("Id Software", "Wolfenstein Enemy Territory"),