doc: pytest: Document the test_bootstage test

Add this test to the documentation. We need to move the import to follow
the main comment so that it renders correctly, and add a code-block
annotation to the example and indent it correctly. Next, neither of the
functions had comments themselves, so document them now.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/pytest/index.rst b/doc/develop/pytest/index.rst
index e2131a2..5bcda1f 100644
--- a/doc/develop/pytest/index.rst
+++ b/doc/develop/pytest/index.rst
@@ -18,5 +18,6 @@
    :maxdepth: 1
 
    test_000_version
+   test_bootstage
    test_net
    test_net_boot
diff --git a/doc/develop/pytest/test_bootstage.rst b/doc/develop/pytest/test_bootstage.rst
new file mode 100644
index 0000000..f8f10e9
--- /dev/null
+++ b/doc/develop/pytest/test_bootstage.rst
@@ -0,0 +1,8 @@
+test_bootstage
+==============
+
+.. automodule:: test_bootstage
+   :synopsis:
+   :member-order: bysource
+   :members:
+   :undoc-members: