Disable explicit TOC rendering in readme (#222)

Latest changes in GitHub make some TOC links no longer work. Also,
GitHub now always has a somewhat hidden TOC in the upper left corner of
the readme, so I think a TOC with non-working links isn't useful.

Pull request: #222

Author: lefou

Readme.adoc

@@ -1,8 +1,5 @@
 = OS-Lib
 :version: 0.9.1
-:toc-placement: preamble
-:toclevels: 3
-:toc:
 :link-geny: https://github.com/com-lihaoyi/geny
 :link-oslib: https://github.com/com-lihaoyi/os-lib
 :link-oslib-gitter: https://gitter.im/lihaoyi/os-lib