Update README.md

[duskmoss]

The binary shows up in src subdirectory of build folder.

[matte-schwartz]

I previously covered the directory change in #1538 but there’s an issue with running gamescope directly out of the build folder in that it won’t pick up the gamescope layer it builds: #1539 so I decided to just drop the line for the time being

[duskmoss]

ooh messy . I'll close this and let you/someone else deal.