ImportError: libxslt.so.1: cannot open shared object file: No such file or directory

One for the documentation more than anything, but anyone trying a `discover()` and getting something like:
```
ImportError: libxslt.so.1: cannot open shared object file: No such file or directory
```
Just as on https://stackoverflow.com/a/40542539/917444:

For Ubuntu

`apt-get install libxslt-dev`

For Centos

`yum install libxslt-devel`
