add db comment (#14)

macros/db_comment.sql

@@ -0,0 +1,13 @@
+{% macro db_comment() %}
+    {% set query %}
+SELECT
+    TO_DATE(MIN(block_timestamp))
+FROM
+    silver.blocks {% endset %}
+    {% set results = run_query(query) %}
+    {% set results_list = results.columns [0].values() [0].strftime('%Y-%m-%d') %}
+    {% set sql %}
+    COMMENT
+    ON database polygon IS 'Lite Mode dataset with recent data only. Min block_timestamp: {{ results_list }} 🌱 ' {% endset %}
+    {% do run_query(sql) %}
+{% endmacro %}