Document caveats around ps:rebuild and tags/tar deployed applications. Closes #2374

The tags and tar plugins do not necessarily build from source, and running `ps:rebuild` can have some unexpected output in certain cases. Rather than try to handle that complexity - it's a lot - documenting the edge cases is the most appropriate way forward.

plugins/ps/subcommands/rebuild

@@ -4,7 +4,7 @@ source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 source "$PLUGIN_AVAILABLE_PATH/ps/functions"
 
 ps_rebuild_cmd() {
-  declare desc="rebuilds app via command line"
+  declare desc="rebuilds an app from source"
   local cmd="ps:rebuild"
   [[ -z $2 ]] && dokku_log_fail "Please specify an app to run the command on"
   ps_rebuild "$2"

plugins/ps/subcommands/rebuildall

@@ -4,7 +4,7 @@ source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 source "$PLUGIN_AVAILABLE_PATH/ps/functions"
 
 ps_rebuildall_cmd() {
-  declare desc="rebuilds all deployed apps via command line"
+  declare desc="rebuilds all apps from source"
   local cmd="ps:rebuildall"
   for app in $(dokku_apps); do
     (is_deployed "$app") && ps_rebuild "$app"