Fix typo in installation.md: correct script name to install_nixl.py (#385)

### Summary

This PR fixes a minor typo in the `installation.md` file where the
installation command incorrectly referenced `install_nixl.sh`. The
correct script name is `install_nixl.py`.

### Changes Made

- Updated `python install_nixl.sh` to `python install_nixl.py` in
installation.md.

### Why This Is Needed

The incorrect script name could lead to confusion or installation errors
for users following the documentation. This change ensures clarity and
accuracy in the setup instructions.

Co-authored-by: Michał Kuligowski <[email protected]>

Author: yafshar

docs/getting_started/installation.md

@@ -107,7 +107,7 @@ Use the following commands to run a Docker image. Make sure to update the versio
 
     ```bash
     cd vllm-gaudi
-    python install_nixl.sh
+    python install_nixl.py
     cd ..
     ```
 
@@ -144,5 +144,5 @@ Use the following commands to run a Docker image. Make sure to update the versio
     pip install -e .
 
     # Build nixl
-    python install_nixl.sh
+    python install_nixl.py
     ```