update README.md

Author: int32bit

algorithms/HouseRobber/README.md

@@ -38,4 +38,6 @@ int rob(int num[], int n) {
 
 ## 扩展
 
-[House Robber II](../HouseRobberII): 当大街是一条环的情况，即第一个和最后一个是相邻的情况
+1. [House Robber](../HouseRobber): 线性的情况
+2. [House Robber II](../HouseRobberII)：线性的情况，首位相连
+3. [House Robber III](../HouseRobberIII)：树形结构

algorithms/HouseRobberII/README.md

@@ -49,4 +49,6 @@ int rob(int *nums, int n)
 
 ## 扩展
 
-[House Robber](../HouseRobber): 无环的情况
+1. [House Robber](../HouseRobber): 线性的情况
+2. [House Robber II](../HouseRobberII)：线性的情况，首位相连
+3. [House Robber III](../HouseRobberIII)：树形结构

algorithms/HouseRobberIII/README.md

@@ -63,6 +63,6 @@ int rob(TreeNode *root) {
 
 ## 参考
 
-1. [House Robber](../HouseRobber)
-2. [House Robber II](../HouseRobberII)
-3. [House Robber III](../HouseRobberIII)
+1. [House Robber](../HouseRobber): 线性的情况
+2. [House Robber II](../HouseRobberII)：线性的情况，首位相连
+3. [House Robber III](../HouseRobberIII)：树形结构