Add info about formation of players in multiplayer

docs/ini-editing/hardcoded-inis/data/missions/formations.ini.md

@@ -6,6 +6,8 @@ title: formations.ini
 
 This file defines formations which can be used by factions in [faction_prop.ini](./faction_prop.ini.md).
 
+The formation `multiplayer_freighter` is hardcoded to be the only formation used by players in multiplayer. When players form up with NPCs in multiplayer, NPCs will virtually fill up this formation's first slots, leaving the player to the remaining slots to use.
+
 ## Syntax
 
 Multiple `[Formation]` blocks can be defined.
@@ -23,4 +25,4 @@ pl_pos = INT, INT, INT ;optional
 | --------- | ----------- |
 | nickname  | How the formation is referred to elsewhere. |
 | pos       | X, Y and Z coordinates relative to the center of the formation. The number of keys here will limit the number of NPCs that can spawn per formation. NPCs spawned by encounters will always try to catch up with the formation leader. Meaning any too big distance between formation members to the current leader will keep them constantly switching to cruise engines. |
-| pl_pos    | X, Y and Z coordinates relative to the center of the formation. |
+| pl_pos    | X, Y and Z coordinates relative to the center of the formation for players in single-player. |