add suggestions in failure message in install script

Adds suggestions to where you can install docker in the case
that the install script fails to install because of the architecture
not being officially supported.

Signed-off-by: Christopher Jones <tophj@linux.vnet.ibm.com>

hack/install.sh

@@ -210,7 +210,11 @@ do_install() {
 		# unofficially supported without available repositories
 		aarch64|arm64|ppc64le|s390x)
 			cat 1>&2 <<-EOF
-			Error: Docker doesn't officially support $architecture and no Docker $architecture repository exists.
+			Error: This install script does not support $architecture, because no
+			$architecture package exists in Docker's repositories.
+
+			Other install options include checking your distribution's package repository
+			for a version of Docker, or building Docker from source.
 			EOF
 			exit 1
 			;;