Update the documentation for the output param

Author: abouelkhair5

gdown/download.py

@@ -120,7 +120,9 @@ def download(
     url: str
         URL. Google Drive URL is also supported.
     output: str
-        Output filename. Default is basename of URL.
+        Output filename/directory. Default is basename of URL.
+        If output ends with separator '/' basename will be kept and the 
+        parameter will be treated as parenting directory. 
     quiet: bool
         Suppress terminal output. Default is False.
     proxy: str