feat: update context file to recommend full table name (#27)

Author: averikitsch

POSTGRESQL.md

@@ -28,3 +28,26 @@ This section covers connecting to a PostgreSQL database instance.
  likely that the user do not have the correct privileges on the PostgreSQL
  database. Database-level permissions (e.g., `SELECT`, `INSERT`) are required
  to execute queries.
+
+---
+
+# Usage Guidelines
+
+## Reusing Project Values
+
+Users may have set project environment variables:
+
+ * `POSTGRES_HOST`: The hostname or IP address of the PostgreSQL server.
+ * `POSTGRES_PORT`: The port number of the PostgreSQL server.
+ * `POSTGRES_DATABASE`: The name of the database to connect to.
+ * `POSTGRES_USER`: The username for authentication.
+ * `POSTGRES_PASSWORD`: The password for authentication.
+
+Instead of prompting the user for these values for specific tool calls, prompt the user to verify reuse a specific value.
+Make sure to not use the environment variable name like `POSTGRES_HOST`, `${POSTGRES_HOST}`, or `$POSTGRES_HOST`. The value can be found by using command: `echo $POSTGRES_HOST`.
+
+## Use Full Table Name Format "DATABASE_NAME.SCHEMA_NAME.TABLE_NAME"
+
+**ALWAYS** use the full table name format, `DATABASE_NAME.SCHEMA_NAME.TABLE_NAME` in the generated SQL when using the `execute_sql` or `postgres__execute_sql` tool.
+* Default to using "public" for the schema name.
+* Use command `echo $POSTGRES_DATABASE` to get the current database value.