bitbake: fetch2: document checkstatus API

The checkstatus semantics are unconventional, so document them.

(Bitbake rev: efb949020215b580e7dc3694c377b18df2fd7e9c)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -1780,7 +1780,11 @@ class Fetch(object):
 
     def checkstatus(self, urls=None):
         """
-        Check all urls exist upstream
+        Check all URLs exist upstream.
+
+        Returns None if the URLs exist, raises FetchError if the check wasn't
+        successful but there wasn't an error (such as file not found), and
+        raises other exceptions in error cases.
         """
 
         if not urls: