Update README_EN.md

Author: yanglbme

solution/1700-1799/1701.Average Waiting Time/README_EN.md

@@ -159,6 +159,26 @@ function averageWaitingTime(customers: number[][]): number {
 }
 ```
 
+#### Rust
+
+```rust
+impl Solution {
+    pub fn average_waiting_time(customers: Vec<Vec<i32>>) -> f64 {
+        let mut tot = 0.0;
+        let mut t = 0;
+
+        for e in customers.iter() {
+            let a = e[0];
+            let b = e[1];
+            t = t.max(a) + b;
+            tot += (t - a) as f64;
+        }
+
+        tot / customers.len() as f64
+    }
+}
+```
+
 #### JavaScript
 
 ```js