make no-install message more helpful

Author: coke

Build.rakumod

@@ -1,3 +1,10 @@
 class Build {
-    BEGIN die "This repository is not intended to be installed.";
+    BEGIN {
+        note q:to/END/;
+            This repository is not intended to be installed!
+            View the latest HTML version at https://docs.raku.org/
+            Command line viewer at https://github.com/raku/rakudoc
+        END
+        die;
+    }
 }