Document how to install ag.exe for Windows using winget

[JFLarvoire]

Hello,

I sent you a direct email last week describing this and other requests with more details.

I submitted to Microsoft a manifest with a link to my build of The Silver Searcher for Windows.
So the Silver Searcher is now installable easily in Window using Microsoft’s new winget package manager. (Intended to become the default package manager in Windows.)

Here's a proposed change to your README.md file, with instructions on how to install ag.exe using winget.

Jean-François Larvoire

[JFLarvoire]

Thanks.

Did you get the mail I sent you to your at greer.fm address on June 24th?
(I sent it from my work address at hpe.com.)
I'd really appreciate your opinion on the other proposals there.

Regards,

Jean-François