Support submodules when building from a gh repo
Docker-DCO-1.1-Signed-off-by: Song Gao (github: songgao)
@@ -194,7 +194,8 @@ The files at ``PATH`` or ``URL`` are called the "context" of the build. The
build process may refer to any of the files in the context, for example when
using an :ref:`ADD <dockerfile_add>` instruction. When a single ``Dockerfile``
is given as ``URL``, then no context is set. When a Git repository is set as
-``URL``, then the repository is used as the context
+``URL``, then the repository is used as the context. Git repositories are
+cloned with their submodules (`git clone --recursive`).
.. _cli_build_examples:
