update gitignore

.gitignore

@@ -16,3 +16,9 @@
 Book/mt-book.bcf
 Book/mt-book.bcf
 Book/mt-book.idx
 Book/mt-book.idx
 Book/mt-book.synctex(busy)
 Book/mt-book.synctex(busy)
+Section06-Neural-Machine-Translation/section06.pdf
+Section06-Neural-Machine-Translation/section06-test.pdf
+Section05-Neural-Networks-and-Language-Modeling/section05.pdf
+Section04-Phrasal-and-Syntactic-Models/section04.pdf
+Section04-Phrasal-and-Syntactic-Models/section04-test.pdf
+Book/mt-book.pdf