runtime.md: only required properties are MUST applied

Address the issue mentioned in:
#405 (comment)

We already doing this in runc as we can run a container
with a config which has `windows` entry. And this is
the right way to handle it.

Signed-off-by: Qiang Huang <[email protected]>

Author: hqhq

runtime.md

@@ -100,10 +100,10 @@ This operation MUST [generate an error](#errors) if it is not provided a path to
 If the ID provided is not unique across all containers within the scope of the runtime, or is not valid in any other way, the implementation MUST [generate an error](#errors) and a new container MUST NOT be created.
 This operation MUST create a new container.
 
-All of the properties configured in [`config.json`](config.md) except for [`process`](config.md#process) MUST be applied.
+All of the required properties configured in [`config.json`](config.md) MUST be applied.
 [`process.args`](config.md#process) MUST NOT be applied until triggered by the [`start`](#start) operation.
 The remaining `process` properties MAY be applied by this operation.
-If the runtime cannot apply a property as specified in the [configuration](config.md), it MUST [generate an error](#errors) and a new container MUST NOT be created.
+If the runtime cannot apply a required property as specified in the [configuration](config.md), it MUST [generate an error](#errors) and a new container MUST NOT be created.
 
 The runtime MAY validate `config.json` against this spec, either generically or with respect to the local system capabilities, before creating the container ([step 2](#lifecycle)).
 Runtime callers who are interested in pre-create validation can run [bundle-validation tools](implementations.md#testing--tools) before invoking the create operation.