Fixes for the smooth deployment of Team edition. (#438)

* Fixes for the smooth deployment of Team edition.
	- Just uncommenting out the lines does not work as expected.
	- the line for context is required for it to work for team edition deployment.
	- Added the subsequent changes in the installation instructions in README.md

* Adding changes as suggested by @ccoenen
  - making the changes more clear in the code block
  - adding more textual clarity in the sentence on what needs to be changed.

README.md

@@ -23,10 +23,13 @@ The following instructions deploy Mattermost in a production configuration using
 
 If you want to install Enterprise Edition, you can skip this section.
 
-To install the team edition, uncomment out these lines in docker-compose.yaml file:
+To install the team edition, change `build: app` to `build:` and uncomment out these lines in `app:` services block to make it look like below in docker-compose.yaml file:
 ```yaml
-args:
-  - edition=team
+app:
+  build:
+    context: app
+    args:
+      - edition=team
 ```
 The `app` Dockerfile will read the `edition` build argument to install Team (`edition = 'team'`) or Enterprise (`edition != team`) edition.
 

docker-compose.yml

@@ -21,7 +21,8 @@ services:
 
   app:
     build: app
-      # uncomment following lines for team edition or change UID/GID
+      # change `build:app` to `build:` and uncomment following lines for team edition or change UID/GID
+      # context: app
       # args:
       #   - edition=team
       #   - PUID=1000