Update Graph.cpp by explaining calibration cache

aidge_export_tensorrt/static/tensorrt_8.6/src/Graph.cpp

@@ -140,7 +140,8 @@ void Graph::datamode(nvinfer1::DataType datatype)
 
 /**
  * @brief Calibrate the graph using the calibration data found inside the `calibration` folder. 
- * This folder should include a `.info` file containing the dimensions of the calibration data, along with the data stored in a `.batch` file
+ * This folder should include a `.info` file containing the dimensions of the calibration data, along with the data stored in a `.batch` file*
+ * Calibration can be expensive, so it is beneficial to generate the calibration data once and then reuse it for subsequent builds of the network. The cache includes the regression cutoff and quantile values used to generate it, and will not be used if these do not match the settings of the current calibrator. However, the network should be recalibrated if its structure changes or if the input data set changes, and it is the responsibility of the application to ensure this.
  * 
  * @param calibration_folder_path Path to the calibration folder.
  * @param cache_file_path Path to the cache file.