Updated docker-compose.md (#1827)

docker-compose.md

@@ -15,7 +15,7 @@ version: '2'
 
 services:
   web:
-    build: .
+    build:
     # build from Dockerfile
       context: ./Path
       dockerfile: Dockerfile
@@ -220,7 +220,7 @@ networks:
 ### Volume
 
 ```yaml
-# Mount host paths or named volumes, specified as sub-options to a service
+# mount host paths or named volumes, specified as sub-options to a service
   db:
     image: postgres:latest
     volumes:
@@ -230,3 +230,15 @@ networks:
 volumes:
   dbdata:
 ```
+
+### User
+
+```yaml
+# specifying user
+user: root
+```
+
+```yaml
+# specifying both user and group with ids
+user: 0:0
+```