docs: clarify that credential discards unrecognised attributes

It was previously unclear how unrecognised attributes are handled.

Signed-off-by: M Hickford <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: hickford

Documentation/git-credential.txt

@@ -160,6 +160,8 @@ empty string.
 Components which are missing from the URL (e.g., there is no
 username in the example above) will be left unset.
 
+Unrecognised attributes are silently discarded.
+
 GIT
 ---
 Part of the linkgit:git[1] suite

Documentation/gitcredentials.txt

@@ -269,6 +269,7 @@ stdout in the same format (see linkgit:git-credential[1] for common
 attributes). A helper is free to produce a subset, or even no values at
 all if it has nothing useful to provide. Any provided attributes will
 overwrite those already known about by Git's credential subsystem.
+Unrecognised attributes are silently discarded.
 
 While it is possible to override all attributes, well behaving helpers
 should refrain from doing so for any attribute other than username and