Fix typos,config paths in kubelet-in-userns.md. Add link to port forwarder implementation (#30410)

* kubelet-in-userns.md: fix typoes

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

* kubelet-in-userns.md: fix unexpected config paths

Referring to `/etc/containerd/config.toml` makes sense only when the user has
read/write permissions to `/etc/containerd/config.toml` in the current mount
namespace, which is not always assumed in the context of this documentation.

The same applies to `/etc/crio/crio.conf`, too.

Partially revert PR 30020.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

* kubelet-in-userns.md: add back the link to example port forwarder implementation

Add back the link to `k3s/pkg/rootlessports/controller.go` removed in PR 30020.

As stated in `{{ <note> }}`, the corresponding section is written for developers
of Kubernetes distros, not for end users.
So we should retain the implementation details here.

Partially revert PR 30020.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

content/en/docs/tasks/administer-cluster/kubelet-in-userns.md

@@ -14,7 +14,7 @@ without root privileges, by using a {{< glossary_tooltip text="user namespace" t
 This technique is also known as _rootless mode_.
 
 {{< note >}}
-This document describes how to run Kubernetes Node components (and hence pods) a non-root user.
+This document describes how to run Kubernetes Node components (and hence pods) as a non-root user.
 
 If you are just looking for how to run a pod as a non-root user, see [SecurityContext](/docs/tasks/configure-pod-container/security-context/).
 {{< /note >}}
@@ -141,6 +141,7 @@ the host with an external port forwarder, such as RootlessKit, slirp4netns, or
 You can use the port forwarder from K3s.
 See [Running K3s in Rootless Mode](https://rancher.com/docs/k3s/latest/en/advanced/#known-issues-with-rootless-mode)
 for more details.
+The implementation can be found in [the `pkg/rootlessports` package](https://github.com/k3s-io/k3s/blob/v1.22.3+k3s1/pkg/rootlessports/controller.go) of k3s.
 
 ### Configuring CRI
 
@@ -152,8 +153,7 @@ containerd or CRI-O and ensure that it is running within the user namespace befo
 
 Running CRI plugin of containerd in a user namespace is supported since containerd 1.4.
 
-Running containerd within a user namespace requires the following configurations
+Running containerd within a user namespace requires the following configurations.
-in `/etc/containerd/containerd-config.toml`.
 
 ```toml
 version = 2
@@ -176,6 +176,9 @@ version = 2
   SystemdCgroup = false
 ```
 
+The default path of the configuration file is `/etc/containerd/config.toml`.
+The path can be specified with `containerd -c /path/to/containerd/config.toml`.
+
 {{% /tab %}}
 {{% tab name="CRI-O" %}}
 
@@ -183,7 +186,7 @@ Running CRI-O in a user namespace is supported since CRI-O 1.22.
 
 CRI-O requires an environment variable `_CRIO_ROOTLESS=1` to be set.
 
-The following configurations (in `/etc/crio/crio.conf`) are also recommended:
+The following configurations are also recommended:
 
 ```toml
 [crio]
@@ -197,6 +200,8 @@ The following configurations (in `/etc/crio/crio.conf`) are also recommended:
   cgroup_manager = "cgroupfs"
 ```
 
+The default path of the configuration file is `/etc/crio/crio.conf`.
+The path can be specified with `crio --config /path/to/crio/crio.conf`.
 {{% /tab %}}
 {{< /tabs >}}