remove pdf, refine html address

README.md

 # 深度学习入门
 
-1. 新手入门 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/fit_a_line/README.html)] [[.pdf](fit_a_line/README.pdf)] [[.src](fit_a_line/)]
-1. 个性化推荐 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/recommender_system/README.html)] [[.pdf](recommender_system/README.pdf)] [[.src](recommender_system/)]
-1. 识别数字 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/recognize_digits/README.html)] [[.pdf](recognize_digits/README.pdf)] [[.src](recognize_digits/)]
-1. 图像分类 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/image_classification/README.html)] [[.pdf](image_classification/README.pdf)] [[.src](classify_images/)]
-1. 词向量 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/word2vec/README.html)] [[.pdf](word2vec/README.pdf)] [[.src](word2vec/)]
-1. 情感分析 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/understand_sentiment/README.html)] [[.pdf](understand_sentiment/README.pdf)] [[.src](understand_sentiment/)]
-1. 理解单词的语义 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/label_semantic_roles/README.html)] [[.pdf](label_semantic_roles/README.pdf)] [[.src](label_semantic_roles/)]
-1. 机器翻译 [[.html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/tree/develop/machine_translation/README.html)] [[.pdf](machine_translation/README.pdf)] [[.src](machine_translation/)]
+1. 新手入门 [[src](fit_a_line/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/fit_a_line/README.html)]
+1. 个性化推荐 [[src](recommender_system/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/recommender_system/README.html)]
+1. 识别数字 [[src](recognize_digits/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/recognize_digits/README.html)]
+1. 图像分类 [[src](classify_images/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/image_classification/README.html)]
+1. 词向量 [[src](word2vec/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/word2vec/README.html)]
+1. 情感分析 [[src](understand_sentiment/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/understand_sentiment/README.html)]
+1. 理解单词的语义 [[src](label_semantic_roles/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/label_semantic_roles/README.html)]
+1. 机器翻译 [[src](machine_translation/)] [[html](http://htmlpreview.github.io/?https://github.com/PaddlePaddle/book/blob/develop/machine_translation/README.html)]
 
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 <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="知识共享许可协议" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" href="http://purl.org/dc/dcmitype/Text" property="dct:title" rel="dct:type">本教程</span> 由 <a xmlns:cc="http://creativecommons.org/ns#" href="http://book.paddlepaddle.org" property="cc:attributionName" rel="cc:attributionURL">PaddlePaddle</a> 创作，采用 <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">知识共享 署名-非商业性使用-相同方式共享 4.0 国际 许可协议</a>进行许可。