Add academic bibliographic references in the README

[fermadeiral]

This PR adds academic bibliographic references in the README. I realized that this information was missing in our repository because of @slarse's comment here.

Currently, there is only @HarisAdzemovic's thesis, but soon we will have @henry-lp's thesis and other related scientific works.

@monperrus, WDYT?

[codecov]

Codecov Report

Merging #152 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #152   +/-   ##
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  Coverage     82.49%   82.49%           
  Complexity      350      350           
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  Files            36       36           
  Lines          1365     1365           
  Branches        198      198           
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  Hits           1126     1126           
  Misses          144      144           
  Partials         95       95           

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[slarse]

I was actually about to suggest this at the same time as adding that comment, but then I didn't for some reason... As a visitor to the repo, I'd definitely be more impressed with some academic references in the README (and let's face it, the top level README is to roughly 95% an advert for the project).

[monperrus]

Great idea thanks @fermadeiral !

we can replace the full bibtex by a link [bibtex] pointing to the bibtex export of Diva.