docs: document the possibility of zombie processes on ssh disconnect for :connect and :enter commands

Apparently terminating the ssh connection that runs 'docker exec' may result in a process leak as the signal isn't propagated properly (moby/moby#9098). Since we cannot fix this, we should document it so that users do not stumble upon the issue unawares.

Closes dokku/dokku-postgres#212

subcommands/enter

@@ -8,6 +8,7 @@ source "$(dirname "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)")/functions"
 service-enter-cmd() {
   #E a bash prompt can be opened against a running service.
   #E filesystem changes will not be saved to disk.
+  #E > NOTE: disconnecting from ssh while running this command may leave zombie processes due to moby/moby#9098
   #E dokku $PLUGIN_COMMAND_PREFIX:enter lollipop
   #E you may also run a command directly against the service.
   #E filesystem changes will not be saved to disk.