Broken manual installation page link

[dedifferentiator]

Reproduction:

• Visit https://scala-android.org/setup/#manual page
• Choose manual installation option at prerequisites
• Open http://www.scala-sbt.org/0.13/docs/Manual-Installation.html which turns out broken.

[eed3si9n]

Not sure when we deleted it since we don't want ppl to do what was documented in the page, which was to roll your own bash script.
A better step would be to grab the latest tgz file from here - https://www.scala-sbt.org/download.html