doc: Add LGTM.com code quality badges
doc: Add LGTM.com code quality badges

Add LGTM.com code quality badges as an incentive for contrinbutors to care about code quality

Signed-off-by: Xavier RENE-CORAIL <8d81151e6adf56c58036acf4c4ca3223a971078d@gmail.com>

db-migrate/node-db-migrate,db-migrate/node-db-migrate