card: pin transformers <5.15 in the install line

README.md

@@ -78,9 +78,13 @@ print(tok.decode(out[0, ids.shape[1]:], skip_special_tokens=False))
 ## Installation
 
 ```bash
-pip install glq
+pip install glq "transformers>=5.13.1,<5.15"
 ```
 
+**Pin transformers below 5.15** — 5.15.0 moved gemma-4 to a per-layer config, so
+`config.head_dim` raises and vLLM dies before loading a single weight. Verified on
+5.14.1 with vLLM 0.27.1. Not specific to GLQ: stock bf16 gemma-4 fails the same way.
+
 The custom CUDA kernel JIT-compiles on first use (~30s). Requires
 `torch>=2.0`, `transformers>=5.0`, CUDA 12.x.