[Feature][Docs] Add Python-only quick install mode (BUILD_WHEEL=2) to build.sh (#6503)

* add pythononly func

* add

* add more feature

* add safe check

* add rsync check

* add

* add

* refine docs

* add installation

* add installation

docs/get_started/installation/nvidia_gpu.md

@@ -125,6 +125,44 @@ After the build completes, the operator binaries can be found in `FastDeploy/fas
 > - For custom architectures or modified operator logic, please use **source compilation (Section 4)**.
 > - You can check whether the precompiled wheel for a specific commit has been successfully built on the [FastDeploy CI Build Status Page](https://github.com/PaddlePaddle/FastDeploy/actions/workflows/ci_image_update.yml).
 
+## 6. Python-only Quick Install (For Development)
+
+If you have already completed a full build (`bash build.sh 1 ...`) and only modified Python files, you can use the python-only mode to quickly sync changes to `site-packages` **without recompiling C++ Custom Ops or rebuilding the wheel**.
+
+### Prerequisites
+
+A full build must have been completed at least once:
+
+```shell
+bash build.sh 1 python false [80,90]
+```
+
+### Usage
+
+```shell
+# Argument 1: Must be 2 to enable python-only mode
+# Argument 2 (optional): Python interpreter path (default: python)
+
+# Use default python
+bash build.sh 2
+
+# Use a specific python interpreter
+bash build.sh 2 python3
+
+# Use an absolute path to the interpreter
+bash build.sh 2 /path/to/your/python
+```
+
+This command syncs `.py` files from the source tree directly into the installed `site-packages/fastdeploy/` directory via `rsync`. Compiled artifacts (`.so` files) are preserved.
+
+### When to Use
+
+| Scenario | Recommended Command |
+|---|---|
+| Only modified Python files | `bash build.sh 2` |
+| Modified C++/CUDA code | `bash build.sh 1 python false [80,90]` |
+| First-time build | `bash build.sh 1 python false [80,90]` |
+
 ## Environment Verification
 
 After installation, verify the environment with this Python code: