Rephrase editor message shown on invalid main sector / spawnpoint and add a translator note to not translate "main" in both cases

Author: tobbi

src/editor/editor.cpp

@@ -1028,11 +1028,17 @@ Editor::check_save_prerequisites(const std::function<void ()>& callback) const
   {
     if (!sector_valid)
     {
-      Dialog::show_message(_("Couldn't find a \"main\" sector.\nPlease change the name of the sector where\nyou'd like the player to start to \"main\""));
+      /*
+      l10n: When translating this message, please keep "main" untranslated (the game expects the name of the sector to be "main").
+      */
+      Dialog::show_message(_("Couldn't find a sector with the name \"main\".\nPlease change the name of the sector where\nyou'd like the player to start to \"main\""));
     }
     else if (!spawnpoint_valid)
     {
-      Dialog::show_message(_("Couldn't find a \"main\" spawnpoint.\n Please change the name of the spawnpoint where\nyou'd like the player to start to \"main\""));
+      /*
+      l10n: When translating this message, please keep "main" untranslated (the game expects the name of the spawnpoint to be "main").
+      */
+      Dialog::show_message(_("Couldn't find a spawnpoint with the name \"main\".\nPlease change the name of the spawnpoint where\nyou'd like the player to start to \"main\""));
     }
   }