add options for compose version in readme

roles/docker/tasks/ubuntu.yml

@@ -1,3 +1,7 @@
+- name: Include variables                                                            
+  include_vars:
+    file: "../../../variables.yml"
+
 - name: Install docker prerequsistes
   apt:
     pkg:
@@ -24,7 +28,7 @@
 #install compose:
 
 - name: download compose
-  shell: curl -L https://github.com/docker/compose/releases/download/1.21.2/docker-compose-`uname -s`-`uname -m` -o /usr/local/bin/docker-compose
+  shell: curl -L https://github.com/docker/compose/releases/download/{{ compose_ver }}/docker-compose-`uname -s`-`uname -m` -o /usr/local/bin/docker-compose
 
 - name: link compose
   shell: chmod +x /usr/local/bin/docker-compose

variables.yml

@@ -2,3 +2,4 @@ users:
   - commonuser
 tinc_vpn: vpn
 hostname: common_hostname
+compose_ver: 1.25.4