doc: update doc build instructions

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/tutorials/docbuild.rst

@@ -34,6 +34,9 @@ The project's documentation contains the following items:
   device-model folders, and from sources in the acrn-kernel repo (as
   explained later).
 
+.. image:: images/doc-gen-flow.png
+   :align: center
+
 The reStructuredText files are processed by the Sphinx documentation system
 and use the breathe extension for including the doxygen-generated API
 material.
@@ -239,12 +242,14 @@ good, you can push directly to the publishing site with:
 
    make publish
 
-This will delete everything in the publishing repo's **latest** folder
-(in case the new version has deleted files) and push a copy of the
-newly-generated HTML content directly to the GitHub pages publishing
-repo.  The public site at https://projectacrn.github.io will be updated
-typically within a few minutes, so it's best to verify the locally
-generated HTML before publishing.
+This uses git commands to synchronize the new content with what's
+already published and will delete files in the publishing repo's
+**latest** folder that are no longer needed. New or changed files from
+the newly-generated HTML content are added to the GitHub pages
+publishing repo.  The public site at https://projectacrn.github.io will
+be updated by the `GitHub pages system
+<https://guides.github.com/features/pages/>`_, typically within a few
+minutes.
 
 Document Versioning
 *******************

doc/tutorials/images/doc-gen-flow.dot

@@ -0,0 +1,23 @@
+# Doc Generation flow
+# dot -Tpng -odoc-gen-flow.png doc-gen-flow.dot
+
+digraph docgen {
+   node [ fontname="verdana"]
+   bgcolor=transparent; rankdir=LR;
+   images [shape="rectangle" label=".png, .jpg\nimages"]
+   rst [shape="rectangle" label="restructuredText\nfiles"]
+   conf [shape="rectangle" label="conf.py\nconfiguration"]
+   rtd [shape="rectangle" label="read-the-docs\ntheme"]
+   header [shape="rectangle" label="c header\ncomments"]
+   xml [shape="rectangle" label="XML"]
+   html [shape="rectangle" label="HTML\nweb site"]
+   sphinx[shape="ellipse" label="sphinx +\nbreathe,\ndocutils"]
+   images -> sphinx
+   rst -> sphinx
+   conf -> sphinx
+   header -> doxygen
+   doxygen -> xml
+   xml-> sphinx
+   rtd -> sphinx
+   sphinx -> html
+   }