Fix running `make doc` on Travis

`make doc` on Travis prints:

    UnicodeEncodeError: 'ascii' codec can't encode characters in position
    416-423: ordinal not in range(128)

This commit tells pydoc that we're expecting UTF-8 on stdout so Unicode
strings should be encoded as UTF-8.  This fixes that issue but I'm
uncertain what else this will have fixed.  It seems like the right thing
to do anyway though.
documentation: Add OCR tips