Updated footer documentation
Updated footer documentation

Updated the documentation of Footer with missing options which it supports.

Signed-off-by: Arjun BM <7b83b400631cbb8df56aeb4a549322db116e1353@gmail.com>
grommet/grommet-docs,karatechops/grommet-docs,grommet/grommet-docs,karatechops/grommet-docs