doc: Expand upgrade notes.

doc/upgrade.md

@@ -3,21 +3,27 @@
 
 ### Docker
 
-Update only the code:
+First ensure that docker is running.
+If `docker ps` returns an error try:
+
+    sudo systemctl start docker
+
+Update only the code (prepend sudo to each docker command if necessary):
 
     basicswap]$ git pull
-    $ cd docker
-    $ export COINDATA_PATH=[PATH_TO]
-    $ docker-compose build
-    $ docker-compose up
+    cd docker
+    export COINDATA_PATH=[PATH_TO]
+    (Probably export COINDATA_PATH=/var/data/coinswaps)
+    docker-compose build
+    docker-compose up
 
 If the dependencies have changed the container must be built with `--no-cache`:
 
     basicswap]$ git pull
-    $ cd docker
-    $ export COINDATA_PATH=[PATH_TO]
-    $ docker-compose build --no-cache
-    $ docker-compose up
+    cd docker
+    export COINDATA_PATH=[PATH_TO]
+    docker-compose build --no-cache
+    docker-compose up
 
 
 #### Update core versions