doc: resolve typos in docs

Fix typo and unify headers in README.md

Signed-off-by: Jieqiang Wang <jieqiang.wang@arm.com>
Reviewed-by: Lijian Zhang <lijian.zhang@arm.com>
Reviewed-by: Tianyu Li <tianyu.li@arm.com>

Change-Id: I3e237662ea091d6679f8f660c4e683f359190256