[Doc] Fix Python-only build 404 fallback guidance (#38052)

Signed-off-by: George-ao <yuyiao772@gmail.com>
Signed-off-by: Yuyi Ao <yuyiao772@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/getting_started/installation/gpu.cuda.inc.md

@@ -107,10 +107,10 @@ This command will do the following:
     1. If you change C++ or kernel code, you cannot use Python-only build; otherwise you will see an import error about library not found or undefined symbol.
     2. If you rebase your dev branch, it is recommended to uninstall vllm and re-run the above command to make sure your libraries are up to date.
 
-In case you see an error about wheel not found when running the above command, it might be because the commit you based on in the main branch was just merged and the wheel is being built. In this case, you can wait for around an hour to try again, or manually assign the previous commit in the installation using the `VLLM_PRECOMPILED_WHEEL_LOCATION` environment variable.
+In case you see an error about wheel not found when running the above command, it might be because the commit you based on in the `main` branch was just merged and its precompiled wheel is not available yet. You can wait around an hour and retry, or set `VLLM_PRECOMPILED_WHEEL_COMMIT=nightly` to automatically select the most recent already-built commit on `main`.
 
 ```bash
-export VLLM_PRECOMPILED_WHEEL_COMMIT=$(git rev-parse HEAD~1) # or earlier commit on main
+export VLLM_PRECOMPILED_WHEEL_COMMIT=nightly
 export VLLM_USE_PRECOMPILED=1
 uv pip install --editable .
 ```