Encoding problem with Suvi Nykäsenoja's name in README

[Peter Cock]

The README file as shown on Bitbucket has a problem with the citation, Suvi Nykäsenoja’s name with the double-dot-a is shown as Nyk�senoja (a black diamond with a question mark). This is probably a copy and paste error, a plain “a” might be an acceptable fall back.

[CGE Helpdesk]

Changed the ä to a