chore(paper): permanent links and README intro

[jeertmans]

Ref: openjournals/joss-reviews#6915

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (59cdf8f) to head (497dca2).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #77   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          976       976           
=========================================
  Hits           976       976           

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[github-actions]

Benchmark results:

Benchmark	before	changes
accumulate_on_transmitters_grid_over_paths_noapprox	34.9 ms	33.8 ms: 1.03x faster
path_method_image	43.7 us	43.0 us: 1.02x faster
path_method_FPT	78.5 us	78.0 us: 1.01x faster
Geometric mean	(ref)	1.02x faster

Benchmark hidden because not significant (2): accumulate_on_transmitters_grid_over_paths_approx, path_method_MPT