Update install-windows.md
Update install-windows.md

Added a little helper text to highlight the use of Msys64 with CMD or Powershell

Closes #11127.

PiperOrigin-RevId: 309765861

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