Add descriptions for uncertainty quantification methods

[djleung]

No description provided.

[klane]

I feel as though the quantile regression docs should either be added to #168 or in a new PR. The MIS regression and SG-MCMC docs should wait until they are implemented.

[codecov]

Codecov Report

Merging #169 (1ce9bdf) into main (40fa7eb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #169   +/-   ##
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  Coverage   22.13%   22.13%           
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  Files           7        7           
  Lines         402      402           
=======================================
  Hits           89       89           
  Misses        313      313           

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[klane]

I feel as though the quantile regression docs should either be added to #168 or in a new PR. The MIS regression and SG-MCMC docs should wait until they are implemented.

I added a note in 2461c59 to indicate that MIS regression and SG-MCMC are coming soon.