Logged paths come from docker image

Right now building the readme looks like this:
```
[manybubbles@localhost docs]$ ./build_docs --doc README.asciidoc
INFO:docker build:Building the docker image that will build the docs. Expect this to take somewhere between a hundred milliseconds and five minutes.
INFO:build_docs:Building HTML from /doc/docs/README.asciidoc
INFO:build_docs:Done
INFO:build_docs:See: /out/html_docs/index.html
```

The trouble is that `/doc` and `/out` are paths in the docker image which isn't at all clear. We should do *something* about this. I'm not really sure what though.