Add additional error output

- When no Spotify client is detected on "non-APT" Linux distros, script will check for spicetify command and, if found, mention that spicetify must not be applied prior to using this script. 

Devices running an APT-supported distro or macOS will be prompted to (re)install the client which resolves the issue so no additional error or warning output should be needed.

spotx.sh

@@ -263,6 +263,7 @@ linux_no_client() {
     return
   }
   echo -e "${red}Error:${clr} Spotify installation not found.\nInstall Spotify or set Spotify directory path with '-P' flag.\n" >&2
+  command -v spicetify >/dev/null && echo -e "If Spotify is installed but Spicetify has been applied,\nrun ${yellow}'spicetify restore'${clr} then try again.\n" >&2
   exit 1
 }