[Docs] Add ocr example

examples/optical_character_recognition/key_information_extraction/README.md

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+# Key Information Extraction Example
+
+## Introduction
+
+![](.data/annotated_ocr_kie_task.png) 
+
+**Key Information Extraction (KIE)** involves extracting essential information from images, such as retrieving a name and ID number from an ID card. The type of information extracted is often specific to the task at hand but can vary across different tasks.
+
+KIE is typically divided into two sub-tasks:
+- **Semantic Entity Recognition (SER)**: Recognizes and classifies text within images.
+- **Relation Extraction (RE)**: Categorizes detected text (e.g., distinguishing questions from answers) and identifies relationships, such as matching questions with their corresponding answers.
+
+## Usage
+
+### Semantic Entity Recognition
+
+For the SER task, you can annotate text regions using the following three methods:
+
+- **Rectangle (Shortcut: R)**: Draws rectangular shapes around text regions.
+- **Rotation (Shortcut: O)**: Annotates text regions with a rotated shape.
+- **Polygon (Shortcut: P)**: Allows for "four-point" or "irregular polygon" annotations.
+
+After drawing the text boxes, fill in the following fields in the label editing dialog:
+- `label`: The entity type, such as QUESTION, ANSWER, HEADER, or OTHER for the [XFUND](https://github.com/doc-analysis/XFUND) dataset.
+- `description`: The specific text content.
+- `difficult`: This field can be toggled via the `useDifficult` checkbox.
+
+### Relation Extraction
+
+![](.data/annotated_ppocr_kie_toturial.gif) 
+
+For the RE task, in addition to the SER fields, you need to fill in two more fields:
+- `group_id`: A unique identifier for each text box within an image.
+- `linking`: Links questions to their corresponding answers, identified by `group_id`.
+
+To modify any of these fields, use `Ctrl+E` to open the label manager and make adjustments in the pop-up dialog.
+
+## Export
+
+For instructions on exporting PP-OCR KIE annotations, please refer to the user guide:
+- [English version](../../docs/en/user_guide.md)
+- [Chinese version](../../docs/zh_cn/user_guide.md)
+
+A complete example of the output can be found [here](./ppocr-kie/).
+
+The exported annotations are suitable for training PP-OCR KIE tasks.

examples/optical_character_recognition/key_information_extraction/ppocr-kie/class_list.txt

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+OTHER
+HEADER
+ANSWER
+QUESTION