Docs for compound primary keys with CLI

docs/cli.rst

@@ -200,6 +200,8 @@ Here's the simplest possible example::
 
 To specify a column as the primary key, use ``--pk=column_name``.
 
+To create a compound primary key across more than one column, use ``--pk`` multiple times.
+
 If you feed it a JSON list it will insert multiple records. For example, if ``dogs.json`` looks like this::
 
     [

sqlite_utils/cli.py

@@ -302,7 +302,7 @@ def insert_upsert_options(fn):
             ),
             click.argument("table"),
             click.argument("json_file", type=click.File(), required=True),
-            click.option("--pk", help="Column to use as the primary key, e.g. id", multiple=True),
+            click.option("--pk", help="Columns to use as the primary key, e.g. id", multiple=True),
             click.option("--nl", is_flag=True, help="Expect newline-delimited JSON"),
             click.option("-c", "--csv", is_flag=True, help="Expect CSV"),
             click.option(