README: split into sections, reformat for github.io

Split the rather large README into smaller sections with a pitch and
a ToC at the top.

Move the sections into docs/ so that Github Pages can read them.

'make doc' produces a local HTML tree.

Update the kernel bugs and gotchas list.

Add some information that has been accumulating in Github comments.

Remove information about bugs in kernels earlier than 4.14.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

docs/Makefile

@@ -0,0 +1,8 @@
+MARKDOWN := $(firstword $(shell type -P markdown markdown2 markdown_py 2>/dev/null || echo markdown))
+.PHONY: docs
+
+docs: $(subst .md,.html,$(wildcard *.md)) ../README.html
+
+%.html: %.md
+	$(MARKDOWN) $< | sed -e 's/\.md/\.html/g' > $@.new
+	mv -f $@.new $@