Add a README to all legacy release and nightly repos to redirect them to binaries repos

[karianna]

Check for all the following repos and add a README telling folks to go to openjdk<version>-binaries instead.

• [x] openjdk8-nightly
• [x] openjdk9-nightly
• [x] openjdk10-nightly
• [x] openjdk8-releases
• [x] openjdk9-releases
• [x] openjdk10-releases
• [x] openjdk8-openj9-nightly
• [x] openjdk9-openj9-nightly
• [x] openjdk10-openj9-nightly
• [x] openjdk8-openj9-releases
• [x] openjdk9-openj9-releases
• [x] openjdk10-openj9-releases

[xtbe]

All repos checked and adapted where needed. PRs submitted