Better description for put_delete_auth_file option

docs/Options.md

@@ -16,7 +16,9 @@ of name=value pairs, like this: `VARIABLE1=VALUE1,VARIABLE2=VALUE2`.
 
 ### put\_delete\_auth\_file
 Passwords file for PUT and DELETE requests. Without it, PUT and DELETE requests
-will fail.
+will fail. The format of the passwords file is the same as `.htpasswd` file
+used for Digest authentication. It can be created and managed by means
+of `mongoose -A ...` command.
 
 ### cgi_interpreter
 Path to an executable to use as CGI interpreter for __all__ CGI scripts