Add example showing the use of `asfoldable` to docs

[codecov[bot]]

Codecov Report

Merging #535 (f2a6829) into master (c8fa4f2) will increase coverage by 0.08%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #535      +/-   ##
==========================================
+ Coverage   95.33%   95.42%   +0.08%     
==========================================
  Files          32       32              
  Lines        2230     2230              
==========================================
+ Hits         2126     2128       +2     
+ Misses        104      102       -2     

Flag	Coverage Δ
Pkg.test	94.55% <ø> (+0.09%)	:arrow_up:
Run.test	95.20% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/core.jl	93.02% <ø> (ø)
src/nondeterministic_threading.jl	90.81% <0.00%> (+2.04%)	:arrow_up:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.