Add flag description for Paddle-TensorRT (#1615)

* Add flag description for Paddle-TensorRT

Many users don't know how to build Paddle-TensorRT duo to lacking
description, so add needed information

* Adjust TENSORRT_ROOT description

* use Simplified Chinese
* put default values on table

doc/fluid/beginners_guide/install/Tables.md

@@ -173,12 +173,18 @@
 		<td> 是否打开预测优化 </td>
 		<td> OFF </td>
 	</tr>
-	</tr>
+	<tr>
 		<tr>
 		<td> CUDA_ARCH_NAME </td>
 		<td> 是否只针对当前CUDA架构编译 </td>
 		<td> All:编译所有可支持的CUDA架构 可选：Auto 自动识别当前环境的架构编译 </td>
 	</tr>
+	<tr>
+		<tr>
+		<td> TENSORRT_ROOT </td>
+		<td> 指定TensorRT路径 </td>
+		<td> Windows下默认值为'/'，Linux下默认值为 '/usr/' </td>
+	</tr>
    </tbody>
 </table>
 </p>

doc/fluid/beginners_guide/install/Tables_en.md

@@ -197,6 +197,16 @@
 		<td> Whether to Compile ANAKIN </td>
 		<td> OFF </td>
 	</tr>
+	<tr>
+		<td> CUDA_ARCH_NAME </td>
+		<td> Build for which GPU architecture </td>
+		<td> All:all available GPU architectures Auto:Automatically detect current GPU architecture </td>
+	</tr>
+	<tr>
+		<td> TENSORRT_ROOT </td>
+		<td> Assign TensoRRT path </td>
+		<td> If this flag is not assigned, Paddle will detect TensorRT automatically. </td>
+	</tr>
    </tbody>
 </table>
 </p>