Include existing elliptic curves docu

[aaruni96]

Includes the elliptic curves documentation already existing under Hecke to be included into doc/main (and then also the search results).

Fixes #4187

As a note, this doesn't build on my local machine. I have the same problem I had in the other PR : #4292 (comment) , the search index is never created, and then the patching step errors out.

[ Info: Patching search index.
sed: can't read /home/aaruni/Programs/git/GitHub/Oscar.jl/docs/build/search_index.js: No such file or directory
ERROR: LoadError: failed process: Process(`sed -n '2p;3q' /home/aaruni/Programs/git/GitHub/Oscar.jl/docs/build/search_index.js`, ProcessExited(2)) [2]

It should still work, in principle. Lets see what the CI says.

[joschmitt]

This file is empty (except for a title). Should we still include it?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.50%. Comparing base (5a737af) to head (d1e4d14).
Report is 238 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4338   +/-   ##
=======================================
  Coverage   84.50%   84.50%           
=======================================
  Files         645      645           
  Lines       85621    85621           
=======================================
  Hits        72354    72354           
  Misses      13267    13267