Merge pull request #497 from wp-cli/regenerate-readme

Regenerate README file

Author: swissspidy

README.md

@@ -398,6 +398,10 @@ wp plugin is-active <plugin> [--network]
 
 Returns exit code 0 when active, 1 when not active.
 
+If the plugin does not exist but is still in WordPress's active plugins storage
+(such as the active plugins option or the sitewide plugins option for network-activated plugins),
+a warning will be emitted.
+
 **OPTIONS**
 
 	<plugin>