docs: add a man-pages link to the front page

Readers looking for user-oriented information may benefit from it.

Signed-off-by: Jonathan Corbet <[email protected]>
Reviewed-by: David Vernet <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

Author: Jonathan Corbet

Documentation/index.rst

@@ -76,6 +76,8 @@ developers seeking information on the kernel's user-space APIs.
    User-space tools <tools/index>
    userspace-api/index
 
+See also: the `Linux man pages <https://www.kernel.org/doc/man-pages/>`_,
+which are kept separately from the kernel's own documentation.
 
 Firmware-related documentation
 ------------------------------