Explain how to install a release build in BUILDING.md

[justinyaodu]

When users run commands with a debug build, they see a warning that debug builds may have worse performance. Add instructions to BUILDING.md so that users who wish to install from source know how to get a release build.

I tested the command locally and ran container --version to verify that I got a release build.

[jglogan]

@justinyaodu Thanks for the contribution! This makes sense.

Since it's necessary for BUILD_CONFIGURATION to be defined consistently across targets, could you amend this so it shows both commands?

BUILD_CONFIGURATION=release make all test integration
BUILD_CONFIGURATION=release make install

Of course you can set BUILD_CONFIGURATION in the environment; you can also set these as make variables (putting BUILD_CONFIGURATION after make) instead of using the environment. We can assume a certain amount of developer expertise with make and variables, just show the release version of these two commands, and let developers figure out what suits them best.

[justinyaodu]

Now that you mention it, I actually did get confused by this. At some point I ran make all with BUILD_CONFIGURATION=release and make install without it, and still got the debug build. Thanks for the great suggestion! I have updated the PR.

[jglogan]

lgtm, thanks!

[jglogan]

lgtm, thanks!