Added missing Oxford (serial) commas in README.md
Added missing Oxford (serial) commas in README.md

A, b ***,*** and c.

Closes #4136.

PiperOrigin-RevId: 177273999

akira-baruah/bazel,dslomov/bazel-windows,akira-baruah/bazel,dslomov/bazel-windows,twitter-forks/bazel,akira-baruah/bazel,davidzchen/bazel,ulfjack/bazel,bazelbuild/bazel,meteorcloudy/bazel,ulfjack/bazel,werkt/bazel,dslomov/bazel-windows,cushon/bazel,dslomov/bazel,davidzchen/bazel,safarmer/bazel,dropbox/bazel,ulfjack/bazel,davidzchen/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,davidzchen/bazel,werkt/bazel,perezd/bazel,dropbox/bazel,cushon/bazel,ButterflyNetwork/bazel,meteorcloudy/bazel,bazelbuild/bazel,katre/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,katre/bazel,cushon/bazel,dropbox/bazel,safarmer/bazel,twitter-forks/bazel,werkt/bazel,ButterflyNetwork/bazel,dslomov/bazel,ButterflyNetwork/bazel,safarmer/bazel,aehlig/bazel,aehlig/bazel,werkt/bazel,ulfjack/bazel,dslomov/bazel,perezd/bazel,aehlig/bazel,dslomov/bazel-windows,perezd/bazel,aehlig/bazel,dslomov/bazel,meteorcloudy/bazel,davidzchen/bazel,ulfjack/bazel,perezd/bazel,meteorcloudy/bazel,katre/bazel,aehlig/bazel,katre/bazel,twitter-forks/bazel,bazelbuild/bazel,meteorcloudy/bazel,dslomov/bazel,werkt/bazel,bazelbuild/bazel,aehlig/bazel,cushon/bazel,bazelbuild/bazel,katre/bazel,cushon/bazel,dslomov/bazel,perezd/bazel,meteorcloudy/bazel,dropbox/bazel,davidzchen/bazel,dropbox/bazel,cushon/bazel,ulfjack/bazel,twitter-forks/bazel,safarmer/bazel,dslomov/bazel,twitter-forks/bazel,dslomov/bazel-windows,twitter-forks/bazel,dslomov/bazel-windows,bazelbuild/bazel,aehlig/bazel,katre/bazel,perezd/bazel,dropbox/bazel,akira-baruah/bazel,safarmer/bazel,werkt/bazel,davidzchen/bazel,perezd/bazel,ulfjack/bazel,meteorcloudy/bazel,safarmer/bazel