[Docx] add language (en/cn) switch links (#4470)

* add install docs

* 修改文档

* 修改文档

docs/quantization/README.md

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+[简体中文](../zh/quantization/README.md)
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 # Quantization
 
 FastDeploy supports various quantization inference precisions including FP8, INT8, INT4, 2-bits, etc. It supports different precision inference for weights, activations, and KVCache tensors, which can meet the inference requirements of different scenarios such as low cost, low latency, and long context.

docs/quantization/online_quantization.md

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+[简体中文](../zh/quantization/online_quantization.md)
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 # Online Quantization
 
 Online quantization refers to the inference engine quantizing weights after loading BF16 weights, rather than loading pre-quantized low-precision weights. FastDeploy supports online quantization of BF16 to various precisions, including: INT4, INT8, and FP8.

docs/quantization/wint2.md

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+[简体中文](../zh/quantization/wint2.md)
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 # WINT2 Quantization
 
 Weights are compressed offline using the [CCQ (Convolutional Coding Quantization)](https://arxiv.org/pdf/2507.07145) method. The actual stored numerical type of weights is INT8, with 4 weights packed into each INT8 value, equivalent to 2 bits per weight. Activations are not quantized. During inference, weights are dequantized and decoded in real-time to BF16 numerical type, and calculations are performed using BF16 numerical type.