Fix doc for create_subprocess_exec (GH-12598)


Add missing `program` argument to asyncio.create_subprocess_exec documentation.
(cherry picked from commit 1328375ad1c91f25a1500945a67b0ef36e387527)

Co-authored-by: Dima Tisnek <dimaqq@gmail.com>
diff --git a/Doc/library/asyncio-subprocess.rst b/Doc/library/asyncio-subprocess.rst
index 0bcf661..af7e36e 100644
--- a/Doc/library/asyncio-subprocess.rst
+++ b/Doc/library/asyncio-subprocess.rst
@@ -56,7 +56,7 @@
 Creating Subprocesses
 =====================
 
-.. coroutinefunction:: create_subprocess_exec(\*args, stdin=None, \
+.. coroutinefunction:: create_subprocess_exec(program, \*args, stdin=None, \
                           stdout=None, stderr=None, loop=None, \
                           limit=None, \*\*kwds)