compactor docs

[owen-d]

Closes #3498

[codecov-io]

Codecov Report

Merging #3543 (113225a) into master (bcbffb1) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3543      +/-   ##
==========================================
- Coverage   63.04%   63.01%   -0.03%     
==========================================
  Files         206      206              
  Lines       17697    17697              
==========================================
- Hits        11157    11152       -5     
- Misses       5538     5542       +4     
- Partials     1002     1003       +1     

Impacted Files	Coverage Δ
pkg/querier/queryrange/limits.go	82.85% <0.00%> (-3.81%)	⬇️
pkg/ingester/checkpoint.go	72.83% <0.00%> (-1.14%)	⬇️
pkg/logql/evaluator.go	90.19% <0.00%> (+0.35%)	⬆️

[kavirajk]

LGTM!