Fix typos in README.md
Fix typos in README.md

Thanks to Thoxvi and tobiasb on GitHub!

GitOrigin-RevId: 7b96457e1d88c3f1842461dff31409d4aa8fb4ae
Change-Id: Ia64f390a8fb12dc20550846ca42182062e7f5bc1

google/fully-homomorphic-encryption,google/fully-homomorphic-encryption