doc: move README.log to HTML documentation

Convert README.log to reStructuredText and add it to the generated HTML
documentation.

Assign doc/develop/logging.rst to the maintainer of LOGGING.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1fd975c..02971c2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -698,6 +698,7 @@
 T:	git https://gitlab.denx.de/u-boot/u-boot.git
 F:	common/log*
 F:	cmd/log.c
+F:	doc/develop/logging.rst
 F:	test/log/
 F:	test/py/tests/test_log.py