add en install doc

ppstructure/docs/installation_en.md

+# Quick installation
+
+- [1. PaddlePaddle 和 PaddleOCR](#1)
+- [2. Install other dependencies](#2)
+  - [2.1  VQA](#21)
+
+
+<a name="1"></a>
+## 1. PaddlePaddle and PaddleOCR
+
+Please refer to [PaddleOCR installation documentation](../../doc/doc_en/installation_en.md)
+
+<a name="2"></a>
+## 2. Install other dependencies
+
+<a name="21"></a>
+### 2.1  VQA
+
+* paddleocr
+
+```bash
+pip3 install paddleocr
+```
+
+* PaddleNLP
+```bash
+git clone https://github.com/PaddlePaddle/PaddleNLP -b develop
+cd PaddleNLP
+pip3 install -e .
+```