Update doc format to indicate asciidoctor
Though asciidoctor is compatible with asciidoc, it does have a couple of
extensions we make use of, and our entire toolchain assumes we're using
that particular implementation. Best to be clear.
@@ -26,7 +26,7 @@ Latest build from master is available at [http://docs.keep.network/tbtc/](http:/
### Building
-Docs are written in [AsciiDoc](http://asciidoc.org/), diagrams in a LaTeX package called [Tikz](https://www.overleaf.com/learn/latex/TikZ_package). To build:
+Docs are written in [AsciiDoctor](http://asciidoctor.org/), diagrams in a LaTeX package called [Tikz](https://www.overleaf.com/learn/latex/TikZ_package). To build:
```sh
cd docs
