Use Markdown-style links in README
Add changes to README.md.in from README.md

From commits fbb1167d9dcd276e06c433b9202c0efba6db2f44 and
93973491ed3134e98a453cd023577ec41670fbcf, which changed README.md but
neglected README.md.in.
Fix typos in README.md.in
Update README.md