Add basic documentation for eigh module

[jturner314]

No description provided.

[codecov]

Codecov Report

Merging #283 (ab4cc02) into master (6de9acc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #283   +/-   ##
=======================================
  Coverage   89.01%   89.01%           
=======================================
  Files          71       71           
  Lines        3578     3578           
=======================================
  Hits         3185     3185           
  Misses        393      393           

Impacted Files	Coverage Δ
lax/src/eigh.rs	94.23% <ø> (ø)
ndarray-linalg/src/eigh.rs	91.83% <ø> (ø)

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