docker: use absolute paths in `-v` example (#7762)

Volume paths must be absolute instead of relative.

pages/common/docker-run.md

@@ -21,7 +21,7 @@
 
 - Run command in a new container with bind mounted volumes:
 
-`docker run -v {{path/to/host_path}}:{{path/to/container_path}} {{image}} {{command}}`
+`docker run -v {{/path/to/host_path}}:{{/path/to/container_path}} {{image}} {{command}}`
 
 - Run command in a new container with published ports: