add text column to explain what the variable is used for

same as https://github.com/apache/airflow/issues/10840 just for Variables.


airflow/www/views.py
"""Base View to set Airflow related properties"""
    from airflow import macros
    route_base = ''
    
    extra_args = {
        'macros': macros,
    }
    def render_template(self, *args, **kwargs):