add WorkshopDL support

Dockerfile

@@ -16,8 +16,11 @@ ENV \
 	# http://steamcommunity.com/dev/managegameservers
 	GLST="" \
 	#
-	# Workshop (require API)
-	WORKSHOPCOLLECTIONID="" \
+	# Workshop server download (require API)
+	WORKSHOP="\${WORKSHOPCOLLECTIONID:-}" \
+	#
+	# Workshop client download (require API)
+	WORKSHOPDL="" \
 	#
 	# Server config
 	GAME="garrysmod" \
@@ -35,7 +38,7 @@ ENV \
 		-tickrate \${TICKRATE} \
 		-maxplayers \${MAXPLAYERS} \
 		-authkey \${AUTHKEY} \
-		+host_workshop_collection \${WORKSHOPCOLLECTIONID} \
+		+host_workshop_collection \${WORKSHOP} \
 		+gamemode \${GAMEMODE} \
 		+map \${MAP} \
 		+servercfgfile \${CONFIG} \

README.md

@@ -67,7 +67,8 @@ docker run -it \
     -e "AUTHKEY=..." \
     -e "GAMEMODE=terrortown" \
     -e "MAP=ttt_minecraft_b5" \
-    -e "WORKSHOPCOLLECTIONID=843519054" \
+    -e "WORKSHOP=843519054" \
+    -e "WORKSHOPDL=843519054" \
     -v ./server.cfg:/opt/steam/garrysmod/cfg/server.cfg \
     hackebein/garrysmod
 ```
@@ -94,6 +95,12 @@ MAXPLAYERS: Max players
 CUSTOMPARAMETERS: additional parameters
 (`Default: `)
 
+WORKSHOP: downloads workshop collection for server
+(`Default: `)
+
+WORKSHOPDL: downloads workshop collection for client before joining
+(`Default: `)
+
 ## More Options
 
 You can found more configuration options on the parent image page [hackebein/srcds](https://hub.docker.com/r/hackebein/srcds)