add instructions how to verify download integrity

scripts/checksums

@@ -4,7 +4,7 @@ main() {
     local filename="infractl-CHECKSUMS"
     pushd bin/ >/dev/null || exit 1
     rm -f "${filename}"
-    shasum -a 512 -- infractl-* > "${filename}"
+    shasum --algorithm 512 -- infractl-* > "${filename}"
     popd >/dev/null || exit 1
 
 }

ui/src/containers/DownloadsPage/UserServiceAccountToken.tsx

@@ -46,11 +46,15 @@ export default function UserServiceAccountToken(): ReactElement {
           example, you may put it in your Go executable directory.
         </p>
         <p className="my-2">
-          Here are the commands to move the file, allow it to execute on an Intel-based Mac, confirm
+          Additionally, you may verify the integrity of the binary by downloading the <code>CHECKSUMS (SHA-512)</code> file.
+        </p>
+        <p className="my-2">
+          Here are the commands to check the integrity, move the file, allow it to execute on an Intel-based Mac, confirm
           its location, and help you learn about its features.
         </p>
         <pre className="border border-base-400 p-4 text-lg whitespace-pre-wrap">
-          $ install ~/Downloads/infractl-darwin-amd64 $GOPATH/bin/infractl
+          $ shasum --check --ignore-missing infractl-CHECKSUMS
+          <br />$ install infractl-darwin-amd64 $GOPATH/bin/infractl
           <br />$ xattr -c $GOPATH/bin/infractl
           <br />$ which infractl
           <br />$ infractl help