Add documentation on handling Context propagation

[alexnederlof]

Took me a while to figure this out, and so I want to save other users the trouble.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @alexnederlof to sign the Salesforce Contributor License Agreement.

[codecov-io]

Codecov Report

Merging #54 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #54   +/-   ##
=========================================
  Coverage     19.45%   19.45%           
  Complexity       25       25           
=========================================
  Files            18       18           
  Lines           437      437           
  Branches         20       20           
=========================================
  Hits             85       85           
  Misses          346      346           
  Partials          6        6

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[alexnederlof]

I signed the CLA but the bot doesn't seem to pick it up?

[rmichela]

Closing and reopening to flag down CLA Bot

[rmichela]

Thanks for updating the docs!