bpo-31378: Document sqlite3.OperationalError exception (GH-7677)

(cherry picked from commit 71ede00f)
Co-authored-by: Zackery Spytz <zspytz@gmail.com>

Doc/library/sqlite3.rst

@@ -821,6 +821,13 @@ Exceptions
    exists, syntax error in the SQL statement, wrong number of parameters
    specified, etc.  It is a subclass of :exc:`DatabaseError`.
 
+.. exception:: OperationalError
+
+   Exception raised for errors that are related to the database's operation
+   and not necessarily under the control of the programmer, e.g. an unexpected
+   disconnect occurs, the data source name is not found, a transaction could
+   not be processed, etc.  It is a subclass of :exc:`DatabaseError`.
+
 
 .. _sqlite3-types: