wsl2: cover custom WSL2 kernels (#21956)

## Description

Many customers wonder whether they can use custom kernels on WSL2 and
whether that's officially supported. Explain it is not, but also clarify
that they can do that at their own risk.

Also provide some helpful suggestins.

## Related issues or tickets

<!-- List applicable reviews (optionally @tag reviewers) -->

- [X] Technical review
- [X] Editorial review
- [X] Product review

---------

Co-authored-by: Allie Sadler <102604716+aevesdocker@users.noreply.github.com>

content/manuals/desktop/features/wsl/_index.md

@@ -109,3 +109,4 @@ Docker Desktop does not require any particular Linux distributions to be install
 - [Explore best practices](best-practices.md)
 - [Understand how to develop with Docker and WSL 2](use-wsl.md)
 - [Learn about GPU support with WSL 2](/manuals/desktop/features/gpu.md)
+- [Custom kernels on WSL](custom-kernels.md)

content/manuals/desktop/features/wsl/custom-kernels.md

@@ -0,0 +1,32 @@
+---
+title: Custom kernels on WSL 
+description: Using custom kernels with Docker Desktop on WSL 2
+keywords: wsl, docker desktop, custom kernel
+tags: [Best practices, troubleshooting]
+---
+
+Docker Desktop depends on several kernel features built into the default
+WSL 2 Linux kernel distributed by Microsoft. Consequently, using a
+custom kernel with Docker Desktop on WSL 2 is not officially supported
+and may cause issues with Docker Desktop startup or operation.
+
+However, in some cases it may be necessary
+to run custom kernels; Docker Desktop does not block their use, and
+some users have reported success using them.
+
+If you choose to use a custom kernel, it is recommended you start
+from the kernel tree distributed by Microsoft from their [official
+repository](https://github.com/microsoft/WSL2-Linux-Kernel) and then add
+the features you need on top of that.
+
+It's also recommended that you:
+- Use the same kernel version as the one distributed by the latest WSL2
+release. You can find the version by running `wsl.exe --system uname -r`
+in a terminal.
+- Start from the default kernel configuration as provided by Microsoft
+from their [repository](https://github.com/microsoft/WSL2-Linux-Kernel)
+and add the features you need on top of that.
+- Make sure that your kernel build environment includes `pahole` and
+its version is properly reflected in the corresponding kernel config
+(`CONFIG_PAHOLE_VERSION`).
+