To install a local build of Proton into Steam, make a new directory in
~/.steam/root/compatibilitytools.d/
with a tool name of your choosing and
place the contents of dist
into that folder. The make install
target will
perform this task for you, installing the Proton build into the Steam folder
for the current user. You will have to restart the Steam client for it to pick
up on a new tool.