Update link for online LDA paper

[dymil]

The old link was broken, as Blei moved from Princeton to Columbia. The code link is also broken, but, alas, I don't know anywhere it's still alive.

[mpenkov]

Thank you for your contribution @dymil ! Congrats on your first PR to gensim 🥇 !!

[jonaschn]

@mpenkov Where is this wiki displayed on the website?
I did not come across this page earlier.
I find the notice regarding running LDA in batch mode really helpful.

@dymil
The code can be found here: https://github.com/blei-lab/onlineldavb/blob/master/onlineldavb.py
The paper URL should better be https://papers.neurips.cc/paper/2010/file/71f6278d140af599e06ad9bf1ba03cb0-Paper.pdf
Otherwise your URL will be outdated when Blei moves from Columbia to somewhere else.

[mpenkov]

@jonaschn https://radimrehurek.com/gensim/wiki.html

Can you make a PR with the new links?

[dymil]

#3142

[jonaschn]

@mpenkov Thanks. The wiki page should (in my opinion) be presented more prominently.
I totally missed this benchmark page although I am using gensim for a while.