Updating AGL LAVA Lab setup page

Updating AGL LAVA Lab setup page

1. Fixing Title formatting.
2. Providing a brief overview about what LAVA Lab.

Bug-AGL: [SPEC-4470]
Signed-off-by: Vinod Ahuja <vahuja@unomaha.edu>
Change-Id: Icebc5796c4396e9bd73ab0cf033ad345e204398c
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/28783
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit a7be1051df95f85eae2a6aedc8631221d48545eb)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/28760