[CI:DOCS] Add note to mappings for user/group userns in build
Add a note to the `--userns-uid-map` and `--userns-gid-map` options in
the `podman build` man page.
Addresses:
@@ -650,6 +650,10 @@ If --userns-gid-map-group is specified, but --userns-uid-map-user is not
specified, `podman` will assume that the specified group name is also a
suitable user name to use as the default setting for this option.
+**NOTE:** When this option is specified by a rootless user, the specified
+mappings are relative to the rootless usernamespace in the container, rather
+than being relative to the host as it would be when run rootful.
+
#### **--userns-gid-map-group**=*group*
Specifies that a GID mapping which should be used to set ownership, at the
@@ -661,6 +665,10 @@ If --userns-uid-map-user is specified, but --userns-gid-map-group is not
specified, `podman` will assume that the specified user name is also a
suitable group name to use as the default setting for this option.
+**NOTE:** When this option is specified by a rootless user, the specified
+mappings are relative to the rootless usernamespace in the container, rather
+than being relative to the host as it would be when run rootful.
+
#### **--uts**=*how*
Sets the configuration for UTS namespaces when the handling `RUN` instructions.
