Add additional err msg to build from source for users who's arch fall…

…s outside of the list (#1792)

Co-authored-by: bnonni <me@bryanwnonni.com>
Co-authored-by: raphjaph <raphjaph@protonmail.com>

install.sh

@@ -113,6 +113,7 @@ if [ -z ${target-} ]; then
     x86_64-Linux) target=x86_64-unknown-linux-gnu;;
     *)
       err 'Could not determine target from output of `uname -m`-`uname -s`, please use `--target`:' $uname_target
+      err 'Please try building from source: https://github.com/casey/ord#building'
     ;;
   esac
 fi