MAINT: add hint on how to deal with outdated cache

src/caosadvancedtools/cache.py

@@ -130,7 +130,8 @@ class AbstractCache(ABC):
             raise RuntimeError(
                 "Cache is corrupt or was created with a future version of this program.")
         elif current_schema < self.get_cache_schema_version():
-            raise RuntimeError("Cache version too old.")
+            raise RuntimeError("Cache version too old. Please remove the current cache file:\n"
+                               + self.db_file)
 
     def get_cache_version(self):
         """