It looks like you're using markdown syntax here, but astropy docs are written in `reStructuredText`.  You can always test the build of your docs locally by running `python setup.py build_sphinx` from the root of the astropy tree.

In this particular case, I think what you want is a double-colon at the end of the paragraph, i.e.:

```
For example , here is a code sample to convert pixel coordinates to world coordinates::
```

And then indent every line of the example by 4 spaces, and remove the backticks.