docs:cdiwadkar16-patch-1 - example for INTERP

Added an example for INTERP functions using the smart meters demo

docs/en/12-taos-sql/10-function.md

@@ -880,6 +880,15 @@ INTERP(expr)
 - Pseudocolumn `_irowts` can be used along with `INTERP` to return the timestamps associated with interpolation points(support after version 3.0.1.4).
 - Pseudocolumn `_isfilled` can be used along with `INTERP` to indicate whether the results are original records or data points generated by interpolation algorithm(support after version 3.0.2.3).
 
+**Example**
+
+- We use the smart meters example used in this documentation to illustrate how to use the INTERP function.
+- We want to downsample every 1 hour and use a linear fill for missing values. Note the order in which the "partition by" clause and the "range", "every" and "fill" parameters are used.
+
+```sql
+SELECT _irowts,INTERP(current) FROM test.meters PARTITION BY TBNAME RANGE('2017-07-22 00:00:00','2017-07-24 12:25:00') EVERY(1h) FILL(LINEAR) 
+```
+
 ### LAST
 
 ```sql