Warn if pleroma cannot be installed

src/freedombone-app-gnusocial

 
     # Currently Pleroma won't install on ARM systems
     # because it uses node-sass which doesn't support ARM
-    if [[ "$(arch)" != "arm"* ]]; then
+    if [[ "$(arch)" == "arm"* ]]; then
+        echo -m $'WARNING: Pleroma currently does not support ARM '
+        echo $'architecture, so it will not be installed'
+    else
         function_check install_nodejs
         install_nodejs pleroma-gnusocial
         install_pleroma "gnusocial" "$GNUSOCIAL_DOMAIN_NAME" "$GNUSOCIAL_BACKGROUND_IMAGE_URL" "$GNUSOCIAL_TITLE"