Add js solution to readme for leetcode problem: no.121

Author: tchx626

solution/0100-0199/0121.Best Time to Buy and Sell Stock/README.md

@@ -83,6 +83,24 @@ class Solution {
 }
 ```
 
+### **JavaScript**
+
+```js
+const maxProfit1 = function (prices) {
+  let min = prices[0];
+  let profit = 0;
+  for (let i = 0; i < prices.length; i++) {
+    if (prices[i] < min) {
+      min = prices[i];
+    }
+    if (profit < prices[i] - min) {
+      profit = prices[i] - min;
+    }
+  }
+  return profit;
+};
+```
+
 ### **...**
 
 ```

solution/0100-0199/0121.Best Time to Buy and Sell Stock/README_EN.md

@@ -73,6 +73,24 @@ class Solution {
 }
 ```
 
+### **JavaScript**
+
+```js
+const maxProfit1 = function (prices) {
+  let min = prices[0];
+  let profit = 0;
+  for (let i = 0; i < prices.length; i++) {
+    if (prices[i] < min) {
+      min = prices[i];
+    }
+    if (profit < prices[i] - min) {
+      profit = prices[i] - min;
+    }
+  }
+  return profit;
+};
+```
+
 ### **...**
 
 ```