(#3826) - document the backoff function option
(#3826) - document the backoff function option

[skip ci]

I decided not to document the `default_back_off` option because
I think users don't actually need it, and it might be more
confusing to document it. Simpler if we just say that the
value always starts at 0.

lakhansamani/pouchdb,asmiller/pouchdb,adamvert/pouchdb,TechnicalPursuit/pouchdb,janraasch/pouchdb,asmiller/pouchdb,Actonate/pouchdb,greyhwndz/pouchdb,mwksl/pouchdb,mainerror/pouchdb,ntwcklng/pouchdb,mikeymckay/pouchdb,cshum/pouchdb,seigel/pouchdb,garrensmith/pouchdb,yaronyg/pouchdb,lukevanhorn/pouchdb,tohagan/pouchdb,cshum/pouchdb,shimaore/pouchdb,cesarmarinhorj/pouchdb,cshum/pouchdb,mikeymckay/pouchdb,nicolasbrugneaux/pouchdb,adamvert/pouchdb,elkingtonmcb/pouchdb,nickcolley/pouchdb,Knowledge-OTP/pouchdb,johnofkorea/pouchdb,yaronyg/pouchdb,tyler-johnson/pouchdb,janraasch/pouchdb,TechnicalPursuit/pouchdb,jhs/pouchdb,shimaore/pouchdb,nicolasbrugneaux/pouchdb,elkingtonmcb/pouchdb,mwksl/pouchdb,cdaringe/pouchdb,jhs/pouchdb,tyler-johnson/pouchdb,willholley/pouchdb,tohagan/pouchdb,ramdhavepreetam/pouchdb,mattbailey/pouchdb,yaronyg/pouchdb,KlausTrainer/pouchdb,willholley/pouchdb,h4ki/pouchdb,Charlotteis/pouchdb,pouchdb/pouchdb,cesarmarinhorj/pouchdb,seigel/pouchdb,mikeymckay/pouchdb,johnofkorea/pouchdb,Charlotteis/pouchdb,marcusandre/pouchdb,Dashed/pouchdb,pouchdb/pouchdb,h4ki/pouchdb,tyler-johnson/pouchdb,callahanchris/pouchdb,nickcolley/pouchdb,seigel/pouchdb,Dashed/pouchdb,cdaringe/pouchdb,tohagan/pouchdb,patrickgrey/pouchdb,TechnicalPursuit/pouchdb,lukevanhorn/pouchdb,patrickgrey/pouchdb,Knowledge-OTP/pouchdb,microlv/pouchdb,ntwcklng/pouchdb,cdaringe/pouchdb,optikfluffel/pouchdb,bbenezech/pouchdb,Actonate/pouchdb,Actonate/pouchdb,lukevanhorn/pouchdb,lakhansamani/pouchdb,janraasch/pouchdb,colinskow/pouchdb,shimaore/pouchdb,johnofkorea/pouchdb,microlv/pouchdb,mattbailey/pouchdb,pouchdb/pouchdb,asmiller/pouchdb,daleharvey/pouchdb,adamvert/pouchdb,h4ki/pouchdb,mattbailey/pouchdb,optikfluffel/pouchdb,bbenezech/pouchdb,nickcolley/pouchdb,Knowledge-OTP/pouchdb,mwksl/pouchdb,willholley/pouchdb,marcusandre/pouchdb,cesarmarinhorj/pouchdb,Dashed/pouchdb,crissdev/pouchdb,garrensmith/pouchdb,greyhwndz/pouchdb,callahanchris/pouchdb,ramdhavepreetam/pouchdb,optikfluffel/pouchdb,microlv/pouchdb,mainerror/pouchdb,Charlotteis/pouchdb,nicolasbrugneaux/pouchdb,garrensmith/pouchdb,p5150j/pouchdb,callahanchris/pouchdb,colinskow/pouchdb,ramdhavepreetam/pouchdb,KlausTrainer/pouchdb,crissdev/pouchdb,elkingtonmcb/pouchdb,p5150j/pouchdb,bbenezech/pouchdb,lakhansamani/pouchdb,jhs/pouchdb,patrickgrey/pouchdb,daleharvey/pouchdb,mainerror/pouchdb,marcusandre/pouchdb,p5150j/pouchdb,ntwcklng/pouchdb,colinskow/pouchdb,greyhwndz/pouchdb,KlausTrainer/pouchdb,crissdev/pouchdb,daleharvey/pouchdb