Fix links that point to the website about page

This page was removed from the website for Gensim 4.

Link instead to the right subsections of the intro page.

Also update the links to https.

README.md

@@ -162,7 +162,7 @@ BibTeX entry:
 
   [citing gensim in academic papers and theses]: https://scholar.google.com/citations?view_op=view_citation&hl=en&user=9vG_kV0AAAAJ&citation_for_view=9vG_kV0AAAAJ:NaGl4SEjCO4C
 
-  [design goals]: http://radimrehurek.com/gensim/about.html
+  [design goals]: https://radimrehurek.com/gensim/intro.html#design-principles
   [RaRe Technologies]: http://rare-technologies.com/wp-content/uploads/2016/02/rare_image_only.png%20=10x20
   [rare\_tech]: //rare-technologies.com
   [Talentpair]: https://avatars3.githubusercontent.com/u/8418395?v=3&s=100

setup.py

@@ -171,7 +171,7 @@ def run(self):
 
 .. _GA: https://github.com/RaRe-Technologies/gensim/actions
 .. _Downloads: https://pypi.python.org/pypi/gensim
-.. _License: http://radimrehurek.com/gensim/about.html
+.. _License: https://radimrehurek.com/gensim/intro.html#licensing
 .. _Wheel: https://pypi.python.org/pypi/gensim
 
 Gensim is a Python library for *topic modelling*, *document indexing* and *similarity retrieval* with large corpora.
@@ -224,7 +224,7 @@ def run(self):
 
 Many scientific algorithms can be expressed in terms of large matrix operations (see the BLAS note above). Gensim taps into these low-level BLAS libraries, by means of its dependency on NumPy. So while gensim-the-top-level-code is pure Python, it actually executes highly optimized Fortran/C under the hood, including multithreading (if your BLAS is so configured).
 
-Memory-wise, gensim makes heavy use of Python's built-in generators and iterators for streamed data processing. Memory efficiency was one of gensim's `design goals <http://radimrehurek.com/gensim/about.html>`_, and is a central feature of gensim, rather than something bolted on as an afterthought.
+Memory-wise, gensim makes heavy use of Python's built-in generators and iterators for streamed data processing. Memory efficiency was one of gensim's `design goals <https://radimrehurek.com/gensim/intro.html#design-principles>`_, and is a central feature of gensim, rather than something bolted on as an afterthought.
 
 Documentation
 -------------