glossary: Remove "leaf" and "hierarchy" from runtime namespace definition

Namespaces are not all hierarchical and processes aren't always in
leaves.  Also punt to config-linux.md for details about namespace
creation, although currently that section doesn't talk much about how
the runtime namespaces relate to new container namespaces [1].

Also mention resource access, because runtime namespaces play a role
even if no new container namespaces are created.  I've used resources
that currently explicitly mention runtime namespaces as examples,
although I think more resources (e.g. root.path and mounts[].source
[2,3]) deserve wording about that as well and would be better examples
if they'd already landed such wording.

Examples of resources retrieved from this namespace include
linux.namespaces[].path and the resctrl psuedo-filesystem used for
`linux.intelRdt`, but Mrunal and Michael didn't want me to include the
examples in the glossary entry (probably because they could go stale).

[1]: opencontainers#795 (comment)
[2]: opencontainers#735 (comment)
[3]: opencontainers@604205e#diff-c9c91c29b41257aea3a3403cc606ad99R65

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

glossary.md

@@ -30,9 +30,7 @@ It reads the [configuration files](#configuration) from a [bundle](#bundle), use
 
 ## <a name="glossaryRuntimeNamespace" />Runtime namespace
 
-On Linux, a leaf in the [namespace][namespaces.7] hierarchy from which the [runtime](#runtime) process is executed.
-New container namespaces will be created as children of the runtime namespaces.
-
+On Linux, the namespaces from which new [container namespaces](#container-namespace) are [created](config-linux.md#namespaces) and from which some configured resources are accessed.
 
 [JSON]: https://tools.ietf.org/html/rfc7159
 [UTF-8]: http://www.unicode.org/versions/Unicode8.0.0/ch03.pdf