Auto merge of #11856 - nerith:doc, r=jdm
Auto merge of #11856 - nerith:doc, r=jdm

README.md: Update keyboard shortcuts

Backspace and Shift-Backspace are no longer used to go backwards and forwards through history.

Instead, Alt+Left Arrow and Alt+Right Arrow are used now.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11856)
<!-- Reviewable:end -->

DominoTree/servo,mbrubeck/servo,sadmansk/servo,saneyuki/servo,pyfisch/servo,dsandeephegde/servo,paulrouget/servo,emilio/servo,ConnorGBrewster/servo,anthgur/servo,pyfisch/servo,pyfisch/servo,cbrewster/servo,KiChjang/servo,notriddle/servo,ConnorGBrewster/servo,KiChjang/servo,rnestler/servo,cbrewster/servo,CJ8664/servo,szeged/servo,cbrewster/servo,CJ8664/servo,cbrewster/servo,nnethercote/servo,mbrubeck/servo,splav/servo,szeged/servo,eddyb/servo,CJ8664/servo,emilio/servo,nnethercote/servo,thiagopnts/servo,DominoTree/servo,paulrouget/servo,larsbergstrom/servo,thiagopnts/servo,splav/servo,szeged/servo,emilio/servo,DominoTree/servo,SimonSapin/servo,nrc/servo,jimberlage/servo,szeged/servo,KiChjang/servo,anthgur/servo,DominoTree/servo,mattnenterprise/servo,mattnenterprise/servo,pyfisch/servo,peterjoel/servo,pyfisch/servo,saneyuki/servo,nrc/servo,anthgur/servo,mbrubeck/servo,pyfisch/servo,dsandeephegde/servo,notriddle/servo,rnestler/servo,fiji-flo/servo,CJ8664/servo,paulrouget/servo,canaltinova/servo,szeged/servo,canaltinova/servo,peterjoel/servo,mbrubeck/servo,paulrouget/servo,splav/servo,larsbergstrom/servo,rnestler/servo,notriddle/servo,DominoTree/servo,rnestler/servo,emilio/servo,DominoTree/servo,thiagopnts/servo,mattnenterprise/servo,notriddle/servo,sadmansk/servo,CJ8664/servo,peterjoel/servo,upsuper/servo,larsbergstrom/servo,saneyuki/servo,peterjoel/servo,peterjoel/servo,saneyuki/servo,ConnorGBrewster/servo,avadacatavra/servo,SimonSapin/servo,canaltinova/servo,notriddle/servo,dsandeephegde/servo,SimonSapin/servo,sadmansk/servo,SimonSapin/servo,notriddle/servo,peterjoel/servo,canaltinova/servo,dati91/servo,thiagopnts/servo,nnethercote/servo,szeged/servo,thiagopnts/servo,thiagopnts/servo,CJ8664/servo,nrc/servo,dsandeephegde/servo,avadacatavra/servo,jimberlage/servo,mattnenterprise/servo,cbrewster/servo,emilio/servo,nnethercote/servo,emilio/servo,nnethercote/servo,paulrouget/servo,jimberlage/servo,fiji-flo/servo,larsbergstrom/servo,sadmansk/servo,eddyb/servo,notriddle/servo,KiChjang/servo,ConnorGBrewster/servo,emilio/servo,KiChjang/servo,fiji-flo/servo,cbrewster/servo,splav/servo,saneyuki/servo,rnestler/servo,dsandeephegde/servo,KiChjang/servo,eddyb/servo,avadacatavra/servo,saneyuki/servo,nrc/servo,DominoTree/servo,saneyuki/servo,paulrouget/servo,DominoTree/servo,fiji-flo/servo,upsuper/servo,jimberlage/servo,fiji-flo/servo,rnestler/servo,SimonSapin/servo,splav/servo,nnethercote/servo,mattnenterprise/servo,KiChjang/servo,upsuper/servo,peterjoel/servo,dsandeephegde/servo,anthgur/servo,szeged/servo,anthgur/servo,mbrubeck/servo,fiji-flo/servo,upsuper/servo,saneyuki/servo,pyfisch/servo,anthgur/servo,mbrubeck/servo,paulrouget/servo,larsbergstrom/servo,splav/servo,eddyb/servo,DominoTree/servo,mattnenterprise/servo,saneyuki/servo,ConnorGBrewster/servo,emilio/servo,pyfisch/servo,ConnorGBrewster/servo,larsbergstrom/servo,dati91/servo,eddyb/servo,upsuper/servo,mattnenterprise/servo,larsbergstrom/servo,nrc/servo,paulrouget/servo,peterjoel/servo,jimberlage/servo,canaltinova/servo,avadacatavra/servo,szeged/servo,KiChjang/servo,jimberlage/servo,eddyb/servo,fiji-flo/servo,splav/servo,CJ8664/servo,KiChjang/servo,cbrewster/servo,thiagopnts/servo,mbrubeck/servo,upsuper/servo,szeged/servo,SimonSapin/servo,avadacatavra/servo,dati91/servo,emilio/servo,nrc/servo,fiji-flo/servo,dati91/servo,anthgur/servo,KiChjang/servo,CJ8664/servo,ConnorGBrewster/servo,peterjoel/servo,dati91/servo,nnethercote/servo,sadmansk/servo,larsbergstrom/servo,pyfisch/servo,ConnorGBrewster/servo,eddyb/servo,paulrouget/servo,szeged/servo,larsbergstrom/servo,splav/servo,rnestler/servo,nnethercote/servo,pyfisch/servo,SimonSapin/servo,sadmansk/servo,sadmansk/servo,nnethercote/servo,avadacatavra/servo,larsbergstrom/servo,upsuper/servo,dati91/servo,jimberlage/servo,paulrouget/servo,avadacatavra/servo,notriddle/servo,saneyuki/servo,DominoTree/servo,notriddle/servo,nrc/servo,eddyb/servo,splav/servo,dati91/servo,cbrewster/servo,sadmansk/servo,thiagopnts/servo,notriddle/servo,canaltinova/servo,dati91/servo,mattnenterprise/servo,avadacatavra/servo,dsandeephegde/servo,jimberlage/servo,anthgur/servo,peterjoel/servo,splav/servo,mbrubeck/servo,rnestler/servo,canaltinova/servo,emilio/servo,jimberlage/servo,SimonSapin/servo,upsuper/servo,nnethercote/servo,canaltinova/servo,dsandeephegde/servo