Fix typo in README.md
Fix typo in README.md

Replace support-4v-demos with the correct
support-v4-demos

Change-Id: I5523a317c5cddac043dad182d73ed9fb0fbf53b2

androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx