doc: Move init-related things out of README

Move this section to rst, changing it just enough so that it builds.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index 0d0e60a..da9643d 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -38,6 +38,7 @@
    distro
    driver-model/index
    environment
+   init
    expo
    cedit
    event