document OPDS

README.md

@@ -1039,6 +1039,27 @@ url parameters:
   * `a` = filesize
   * uppercase = reverse-sort; `M` = oldest file first
 
+# opds feeds
+
+browse and download files from your e-book reader
+
+enabled with the `opds` volflag or `--opds` global option
+
+add `?opds` to the end of the url you would like to browse, then input that in your opds client.
+for example: `https://copyparty.example/books/?opds`.
+
+to log in with a password, enter it into either of the username or password fields in your client.
+
+- if you've enabled `--usernames`, then you need to enter both username and password .
+
+note: some clients (e.g. Moon+ Reader) will not send the password when downloading cover images, which will
+cause your ip to be banned by copyparty. to work around this, you can grant the [`g` permission](#accounts-and-volumes)
+to unauthenticated requests and enable [filekeys](#filekeys) to prevent guessing filenames. for example:
+`-vbooks:books:r,ed:g:c,fk,opds`
+
+by default, not all file types will be listed in opds feeds. to change this, add the extension to 
+`--opds-allowed` (volflag: `opds_allowed`), or empty the list to list everything
+
 
 ## recent uploads