Remove non-ASCII characters from README.rst

[akosiaris]

Replace the 2 EN-DASH (https://www.compart.com/en/unicode/U+2013) characters in
README.rst with the ASCII character HYPNEN-MINUS
(http://www.fileformat.info/info/unicode/char/2d/index.htm). Strictly speaking,
the EN-DASH character is more correct but using a non ASCII character can lead
to problems when installing the package like exception thrown by pip running
setup.py like

UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 1200:
ordinal not in range(128)

Of course the problem itself is probably due to the environment for whatever
reason not supporting UTF-8 and/or the setup.py script, but this is all probably
irrelevant and causing undue stress to the end-user wanting to just install this
package.

[jaraco]

Strictly speaking, the EN-DASH character is more correct but using a non ASCII character can lead
to problems

In that case, I'd recommend a different fix.

[jaraco]

I note this would fix #30.

[akosiaris]

@jaraco, what different fix would you recommend?

FWIW, the "more correct" part in my comment is about how a dash is semantically better than the minus ascii sign (which is also a hyphen complicating things even more). But that's semantics and while I thought it worthwhile to note it, it's a very very very very minor issue and I really don't think that it should stand in the way of fixing #30 which clearly is causing issues to people.

[jaraco]

@akosiaris See #36 for what I recommend.

[akosiaris]

@jaraco Yeah, I guess the approach in #36 is fine as well. I don't have a preference as long as one of the two gets merged, so I 'll close #35 in favor of #36