Documentation: Add make rule for sphinx-autobuild

Add livesphinx to start sphinx-autobuild

Change-Id: I9eb3217e758c2c882c759fa7ae75a39aaf1a0358
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/28210
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

Documentation/Makefile

@@ -74,3 +74,6 @@ clean: clean-sphinx
 
 distclean: clean
 	rm -f corebootPortingGuide.pdf Kconfig.pdf
+
+livesphinx:
+	$(MAKE) -f Makefile.sphinx livehtml

Documentation/Makefile.sphinx

@@ -4,6 +4,7 @@
 # You can set these variables from the command line.
 SPHINXOPTS        =
 SPHINXBUILD       = sphinx-build
+SPHINXAUTOBUILD   = sphinx-autobuild
 PAPER             =
 BUILDDIR          = _build
 
@@ -54,6 +55,12 @@ html:
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
 
+.PHONY: livehtml
+livehtml:
+	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)
+	@echo
+	@echo "Autobuild finished. The HTML pages are in $(BUILDDIR)."
+
 .PHONY: dirhtml
 dirhtml:
 	$(SPHINXBUILD) -b dirhtml $(ALLSPHINXOPTS) $(BUILDDIR)/dirhtml