Typo on "How to build OVMF" into the wiki

[darcosion]

Hello,

Just a quick issue to report a typo where I spend half an hour to find "OVMF" (mainly because of my skill issue).

Last sentence :

If successful, you should now have a OVMF.Fd file under the Build sub-directory. The exact directory under the Build directory will depend upon the toolchain, dsc and processor architecture.

It's an "OVMF.fd" if you want to fix

Best regards,
darcosion

[darcosion]

I found the wiki and did a merge request here : tianocore/tianocore-wiki#2