Add code demo for pruning api. (#54)

docs/docs/api/prune_api.md

@@ -307,6 +307,28 @@ paddleslim.prune.merge_sensitive(sensitivities)[源代码](https://github.com/Pa
 
 示例：
 
+```
+from paddleslim.prune import merge_sensitive
+sen0 = {"weight_0":
+   {0.1: 0.22,
+    0.2: 0.33
+   },
+ "weight_1":
+   {0.1: 0.21,
+    0.2: 0.4
+   }
+}
+sen1 = {"weight_0":
+   {0.3: 0.41,
+   },
+ "weight_2":
+   {0.1: 0.10,
+    0.2: 0.35
+   }
+}
+sensitivities = merge_sensitive([sen0, sen1])
+print(sensitivities)
+```
 
 ## load_sensitivities
 paddleslim.prune.load_sensitivities(sensitivities_file)[源代码](https://github.com/PaddlePaddle/PaddleSlim/blob/develop/paddleslim/prune/sensitive.py#L184)
@@ -323,6 +345,24 @@ paddleslim.prune.load_sensitivities(sensitivities_file)[源代码](https://githu
 
 示例：
 
+```
+import pickle
+from paddleslim.prune import load_sensitivities
+sen = {"weight_0":
+   {0.1: 0.22,
+    0.2: 0.33
+   },
+ "weight_1":
+   {0.1: 0.21,
+    0.2: 0.4
+   }
+}
+sensitivities_file = "sensitive_api_demo.data"
+with open(sensitivities_file, 'w') as f:
+    pickle.dump(sen, f)
+sensitivities = load_sensitivities(sensitivities_file)
+print(sensitivities)
+```
 
 ## get_ratios_by_loss
 paddleslim.prune.get_ratios_by_loss(sensitivities, loss)[源代码](https://github.com/PaddlePaddle/PaddleSlim/blob/develop/paddleslim/prune/sensitive.py#L206)
@@ -338,3 +378,22 @@ paddleslim.prune.get_ratios_by_loss(sensitivities, loss)[源代码](https://gith
 返回：
 
 - **ratios(dict)** - 一组剪切率。`key`是待剪裁参数的名称。`value`是对应参数的剪裁率。
+
+示例：
+
+```
+from paddleslim.prune import get_ratios_by_loss
+sen = {"weight_0":
+   {0.1: 0.22,
+    0.2: 0.33
+   },
+ "weight_1":
+   {0.1: 0.21,
+    0.2: 0.4
+   }
+}
+
+ratios = get_ratios_by_loss(sen, 0.3)
+print(ratios)
+
+```