add callbacks to docs

[adamgayoso]

No description provided.

[codecov]

Codecov Report

Merging #1364 (c82aa51) into master (fb99341) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1364   +/-   ##
=======================================
  Coverage   90.86%   90.86%           
=======================================
  Files         109      109           
  Lines        8290     8290           
=======================================
  Hits         7533     7533           
  Misses        757      757           

Impacted Files	Coverage Δ
scvi/train/__init__.py	100.00% <100.00%> (ø)

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