docs: Add documentation for mod_target_category (#4235)

Add documentation for mod_target_category

doc/src/content/docs/en/mod/json/reference/json_info.md

@@ -1930,7 +1930,8 @@ Gun mods can be defined like this:
 ...                            // Same entries as above for the generic item.
                                // Additionally some gunmod specific entries:
 "location": "stock",           // Mandatory. Where is this gunmod is installed?
-"mod_targets": [ "crossbow" ], // Mandatory. What kind of weapons can this gunmod be used with?
+"mod_targets": [ "crossbow" ], // Mandatory. What specific weapons can this gunmod be used with?
+"mod_target_category": [ [ "BOWS" ] ], // Optional. What specific weapon categories can this gunmod be used with?
 "acceptable_ammo": [ "9mm" ],  // Optional filter restricting mod to guns with those base (before modifiers) ammo types
 "install_time": "30 s",        // Optional time installation takes. Installation is instantaneous if unspecified. An integer will be read as moves or a time string can be used.
 "ammo_modifier": [ "57" ],     // Optional field which if specified modifies parent gun to use these ammo types