Add recommendation to use musl libc target to readme

[tomaszjonak]

Since we depend on a shim c layer differences in GLIBC versions may matter if build and runtime environments are different enough. This may result in errors akin to the following.

./demo_socket_listen: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.33' not found (required by ./demo_socket_listen)
./demo_socket_listen: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by ./demo_socket_listen)
./demo_socket_listen: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by ./demo_socket_listen)

If app deployment is containerized it shouldn't matter as the user controls libc version. Still calling this out explicitly wont hurt.