[ci skip] Improve docs for `new-window` event
[ci skip] Improve docs for `new-window` event

This should help clarify the purpose of `event.newGuest` as per the recent discussion in #7407.
thomsonreuters/electron,miniak/electron,shiftkey/electron,wan-qy/electron,rajatsingla28/electron,biblerule/UMCTelnetHub,thomsonreuters/electron,electron/electron,thomsonreuters/electron,wan-qy/electron,electron/electron,wan-qy/electron,biblerule/UMCTelnetHub,electron/electron,joaomoreno/atom-shell,wan-qy/electron,thomsonreuters/electron,rajatsingla28/electron,bpasero/electron,electron/electron,Floato/electron,the-ress/electron,the-ress/electron,tonyganch/electron,thompsonemerson/electron,renaesop/electron,gerhardberger/electron,renaesop/electron,renaesop/electron,miniak/electron,seanchas116/electron,joaomoreno/atom-shell,rajatsingla28/electron,Floato/electron,joaomoreno/atom-shell,bpasero/electron,biblerule/UMCTelnetHub,twolfson/electron,Floato/electron,tonyganch/electron,renaesop/electron,bpasero/electron,twolfson/electron,gerhardberger/electron,the-ress/electron,tonyganch/electron,joaomoreno/atom-shell,rreimann/electron,Floato/electron,miniak/electron,miniak/electron,rreimann/electron,thompsonemerson/electron,rreimann/electron,miniak/electron,Floato/electron,biblerule/UMCTelnetHub,shiftkey/electron,rreimann/electron,joaomoreno/atom-shell,joaomoreno/atom-shell,gerhardberger/electron,rajatsingla28/electron,thomsonreuters/electron,shiftkey/electron,thompsonemerson/electron,tonyganch/electron,rajatsingla28/electron,miniak/electron,tonyganch/electron,thompsonemerson/electron,the-ress/electron,the-ress/electron,gerhardberger/electron,bpasero/electron,tonyganch/electron,wan-qy/electron,thompsonemerson/electron,biblerule/UMCTelnetHub,thompsonemerson/electron,shiftkey/electron,electron/electron,renaesop/electron,bpasero/electron,seanchas116/electron,biblerule/UMCTelnetHub,electron/electron,twolfson/electron,seanchas116/electron,seanchas116/electron,shiftkey/electron,rreimann/electron,brenca/electron,bpasero/electron,shiftkey/electron,seanchas116/electron,seanchas116/electron,brenca/electron,rreimann/electron,bpasero/electron,gerhardberger/electron,brenca/electron,brenca/electron,twolfson/electron,brenca/electron,brenca/electron,gerhardberger/electron,thomsonreuters/electron,the-ress/electron,twolfson/electron,rajatsingla28/electron,electron/electron,Floato/electron,wan-qy/electron,twolfson/electron,gerhardberger/electron,renaesop/electron,the-ress/electron