Add FAQ for docker pull error on Kylin OS (#3870)

Added instructions for resolving 'invalid tar header' error on Kylin OS with an ARM64 architecture on Atlas300I hardware during docker
pull, including steps for offline loading of docker images.

---

### What this PR does / why we need it?

The primary motivation for this PR is to address a critical `docker
pull` failure that occurs on specific, yet important, enterprise
environments. Specifically, when operating on **Kylin OS (麒麟操作系统) with
an ARM64 architecture on Atlas300I hardware**, users frequently
encounter an `archive/tar: invalid tar header` error, which completely
blocks the setup process. This issue has been consistently reproduced,
with multiple retries failing with the same error, confirming that it is
a persistent environmental problem rather than a transient network
issue.

<img width="2060" height="525" alt="image"
src="https://github.com/user-attachments/assets/6c1c5728-de27-476f-8df4-723564fc290b"
/>

This guide provides a robust, step-by-step workaround using an
offline-loading method (`docker save` on a host machine and `docker
load` on the target machine). This solution is crucial for enabling
users on this platform to use vLLM.

This contribution does not directly fix an existing issue number, but it
proactively solves a significant environmental and usability problem for
a growing user base.

### Does this PR introduce _any_ user-facing change?

No.It does not alter any code, APIs, interfaces, or existing behavior of
the vLLM project.

### How was this patch tested?

The instructions and troubleshooting steps in this guide were validated
through a real-world, end-to-end test case on the my hardware and OS.

The testing process was as follows:

1. **Problem Reproduction**: An attempt was made to directly `docker
pull` the `vllm-ascend:v0.10.0rc1-310p` image on a target machine
running Kylin OS (ARM64). The `invalid tar header` failure was
successfully and consistently reproduced, confirming the existence of
the problem.
2. **Solution Implementation**: The workaround detailed in the guide was
executed:
* On a separate host machine (Ubuntu x86_64), the image was successfully
pulled using the `--platform linux/arm64` flag.
* The image was then saved to a `.tar` archive using `docker save`.
* The `.tar` archive was transferred to the target Kylin OS machine.
* The image was successfully loaded from the archive using `docker load
-i ...`.
3. **End-to-End Validation**: After loading the image, the vLLM
container was launched on the target machine following the instructions
in the guide. Both online inference (via `curl` to the API server) and
offline inference (via the Python script) were executed successfully,
confirming that the entire workflow described in the document is
accurate and effective.

Since this is a documentation-only change based on a validated workflow,
no new unit or integration tests were added to the codebase.


- vLLM version: v0.11.0rc3
- vLLM main:
83f478bb19

---------

Signed-off-by: Liwx <liweixuan1014@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

docs/source/faqs.md

@@ -212,3 +212,30 @@ The current stream requirement calculation for size captures only accounts for m
 
 ### 19. How to install custom version of torch_npu?
 torch-npu will be overridden  when installing vllm-ascend. If you need to install a specific version of torch-npu, you can manually install the specified version of torch-npu after vllm-ascend is installed.
+
+### 20. On certain systems (e.g., Kylin OS), `docker pull` may fail with an `invalid tar header` error
+
+On certain operating systems, such as Kylin OS , you may encounter an `invalid tar header` error during the `docker pull` process:
+
+```text
+failed to register layer: ApplyLayer exit status 1 stdout: stderr: archive/tar: invalid tar header
+```
+
+This is often due to system compatibility issues. You can resolve this by using an offline loading method with a second machine.
+
+1. On a separate host machine (e.g., a standard Ubuntu server), pull the image for the target ARM64 architecture and package it into a `.tar` file.
+
+   ```bash
+   export IMAGE_TAG=v0.10.0rc1-310p
+   export IMAGE_NAME="quay.io/ascend/vllm-ascend:${IMAGE_TAG}"
+   # If in China region, uncomment to use a mirror:
+   # export IMAGE_NAME="m.daocloud.io/quay.io/ascend/vllm-ascend:${IMAGE_TAG}"
+   
+   # Pull the image for the ARM64 platform and save it
+   docker pull --platform linux/arm64 "${IMAGE_NAME}"
+   docker save -o "vllm_ascend_${IMAGE_TAG}.tar" "${IMAGE_NAME}"
+   ```
+
+2. Transfer the image archive
+
+Copy the `vllm_ascend_<tag>.tar` file (where `<tag>` is the image tag you used) to your target machine