Create table if_not_exists=True argument, closes #397

docs/python-api.rst

@@ -522,7 +522,9 @@ This will create a table with the following schema:
 Explicitly creating a table
 ---------------------------
 
-You can directly create a new table without inserting any data into it using the ``.create()`` method::
+You can directly create a new table without inserting any data into it using the ``.create()`` method:
+
+.. code-block:: python
 
     db["cats"].create({
         "id": int,
@@ -534,6 +536,17 @@ The first argument here is a dictionary specifying the columns you would like to
 
 This method takes optional arguments ``pk=``, ``column_order=``, ``foreign_keys=``, ``not_null=set()`` and ``defaults=dict()`` - explained below.
 
+A ``sqlite_utils.utils.sqlite3.OperationalError`` will be raised if a table of that name already exists.
+
+To do nothing if the table already exists, add ``if_not_exists=True``:
+
+.. code-block:: python
+
+    db["cats"].create({
+        "id": int,
+        "name": str,
+    }, pk="id", if_not_exists=True)
+
 .. _python_api_compound_primary_keys:
 
 Compound primary keys