Fix & add notes regarding problematic language in codebase

Podman is committed to inclusivity, a core value of open source. Historically, there have been technology terms that are problematic and divisive, and should be changed. We are currently taking time to audit our repository in order to eliminate such terminology, and replace it with more inclusive terms. We are starting where we can, with our own code, comments, and documentation. However, such terms may be used in dependencies, and must be used in our repositories at the current moment for compatibility. Podman will change these terms in our repo as soon as new and better terminology is available to us via our dependencies.

For more information: https://www.redhat.com/en/blog/making-open-source-more-inclusive-eradicating-problematic-language?sc_cid=701600000011gf0AAA

Signed-off-by: Ashley Cui <acui@redhat.com>

rootless.md

@@ -30,7 +30,7 @@ can easily fail
 * Only other supported driver is VFS.
 * No CNI Support
   * CNI wants to modify IPTables, plus other network manipulation that requires CAP_SYS_ADMIN.
-  * There is potential we could probably do some sort of blacklisting of the relevant plugins, and add a new plugin for rootless networking - slirp4netns as one example and there may be others
+  * There is potential we could probably do some sort of denylisting of the relevant plugins, and add a new plugin for rootless networking - slirp4netns as one example and there may be others
 * Cannot use ping out of the box.
   * [(Can be fixed by setting sysctl on host)](https://github.com/containers/libpod/blob/master/troubleshooting.md#6-rootless-containers-cannot-ping-hosts)
 * Requires new shadow-utils (not found in older (RHEL7/Centos7 distros) Should be fixed in RHEL7.7 release)