README: update to cm-10.2 branch

Change-Id: I340f994886c5e2cf365888103257697aeeaa875f
Signed-off-by: Rohan Mathur <rohanmathur34@gmail.com>
default: Add Focal repos to the manifest

Change-Id: I5fa821d8541d10a553a0df94fe49dd18f24f8c0b