Update README to document METEOR_TEST_PACKAGES [ci skip]
Update README to document METEOR_TEST_PACKAGES [ci skip]

serut/spacejam,practicalmeteor/spacejam,serut/spacejam,serut/spacejam,Opstarts/spacejam,practicalmeteor/spacejam,practicalmeteor/spacejam,Opstarts/spacejam,Opstarts/spacejam