Docs update suggestion for installation on Ubuntu 22.04 and lower

I'm not sure that this is the correct way to suggest docs changes there in issues, but

bpftrace version from apt on Ubuntu 22.04 jammy is (0.14.0). For my project I needed at least 0.17.x (strcontains function), so I've decided to build it from sources.

I've followed instructions from INSTALL.md, but faced a problem with libbpf: manual suggests installing it from apt, as in the Dockerfile.ubuntu, but for Ubuntu 22.04 version is 0.5.0, when 1.0 is required for bpftrace.

My suggestion is to add instructions for installing libbpf from sources for Ubuntu 22.04 and lower. For Ubuntu 24.10+ apt installes latest 0.21.x, so the problem doesn't occur.