Add glibc version 2.28+ limitation for using opm

If the linux has not glibc more than v2.28,
you can face "error /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found (required by ./opm)" error, when you run the "opm".
And podman version is recommended 2.0+ for suppressing potential bug implication.

Reference: https://bugzilla.redhat.com/show_bug.cgi?id=1892004#c3
           https://bugzilla.redhat.com/show_bug.cgi?id=1894167

modules/olm-installing-opm.adoc

@@ -16,7 +16,9 @@ You can install the `opm` CLI tool on your Linux, macOS, or Windows workstation.
 
 .Prerequisites
 
-* `podman` version 1.4.4+
+* For Linux, you must provide the following packages:
+** `podman` version 1.4.4+ (version 2.0+ recommended)
+** `glibc` version 2.28+
 
 .Procedure