docs: fix broken quantize_ link in first_quantization_example (#4317)

* docs: fix broken quantize_ link in first_quantization_example

The quantize_ hyperlink in the first sentence referenced an absolute URL
missing the 'api_reference/' path segment. This is a relative link fix
that keeps the reference version-agnostic and consistent with the other
link fixes in PR #4291.

Closes #4286

* chore: empty commit to re-trigger Meta CLA check after signing

Author: Anai-Guo

docs/source/eager_tutorials/first_quantization_example.rst

@@ -1,7 +1,7 @@
 First Quantization Example
 ==========================
 
-The main entry point for quantization in torchao is the `quantize_ <https://pytorch.org/ao/stable/generated/torchao.quantization.quantize_.html#torchao.quantization.quantize_>`__ API.
+The main entry point for quantization in torchao is the `quantize_ <../api_reference/generated/torchao.quantization.quantize_.html#torchao.quantization.quantize_>`__ API.
 This function mutates your model inplace based on the quantization config you provide.
 All code in this guide can be found in this `example script <https://github.com/pytorch/ao/blob/main/scripts/quick_start.py>`__.