Touch up small typo in README.md
Touch up small typo in README.md

Signed-off-by: TomSweeneyRedHat <tsweney@redhat.com>

Closes: #129
Approved by: rhatdan

nalind/buildah,rhatdan/buildah,nalind/buildah-1,rhatdan/buildah,nalind/buildah-1,nalind/buildah,projectatomic/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,ipbabble/buildah,ipbabble/buildah,nalind/buildah-1