Merge pull request #3750 from kinvolk/rata/idmap-merged

docs: Update spec conformance for idmap mounts

Author: AkihiroSuda

docs/spec-conformance.md

@@ -11,10 +11,15 @@ v1.0.0       | `SCMP_ARCH_PARISC`                       | Unplanned, due to lack
 v1.0.0       | `SCMP_ARCH_PARISC64`                     | Unplanned, due to lack of users
 v1.0.2       | `.linux.personality`                     | [#3126](https://github.com/opencontainers/runc/pull/3126)
 v1.1.0-rc.1  | `.linux.resources.cpu.burst`             | [#3749](https://github.com/opencontainers/runc/pull/3749)
-v1.1.0-rc.1  | `.[]mounts.uidMappings`                  | [#3717](https://github.com/opencontainers/runc/pull/3717)
-v1.1.0-rc.1  | `.[]mounts.gidMappings`                  | [#3717](https://github.com/opencontainers/runc/pull/3717)
 v1.1.0-rc.1  | `SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV` | [#3862](https://github.com/opencontainers/runc/pull/3862)
 v1.1.0-rc.2  | time namespaces                          | [#3876](https://github.com/opencontainers/runc/pull/3876)
 v1.1.0-rc.2  | rsvd hugetlb cgroup                      | TODO ([#3859](https://github.com/opencontainers/runc/issues/3859))
 v1.1.0-rc.3  | `.process.scheduler`                     | TODO ([#3895](https://github.com/opencontainers/runc/issues/3895))
 v1.1.0-rc.3  | `.process.ioPriority`                    | [#3783](https://github.com/opencontainers/runc/pull/3783)
+
+
+The following features are implemented with some limitations:
+Spec version | Feature                                  | Limitation
+-------------|------------------------------------------|----------------------------------------------------------
+v1.1.0-rc.1  | `.[]mounts.uidMappings`                  | Requires using UserNS with identical uidMappings
+v1.1.0-rc.1  | `.[]mounts.gidMappings`                  | Requires using UserNS with identical gidMappings