Add omitted documentation line.
@@ -81,6 +81,8 @@ Suppose that `file1.tsv` contains the following table in KGTK format:
| steve | zipcode | 45601 | work | 2 |
| steve | zipcode | 45601 | cabin | |
+Add an ID column using the default ID style (prefixed)
+
```bash
kgtk add_id file1.tsv
```
