rust solution added to README

Author: K11E3R

solution/3100-3199/3100.Water Bottles II/README.md

@@ -156,6 +156,25 @@ function maxBottlesDrunk(numBottles: number, numExchange: number): number {
 }
 ```
 
+#### Rust
+
+```rust
+impl Solution {
+    pub fn max_bottles_drunk(mut num_bottles: i32, mut num_exchange: i32) -> i32 {
+        let mut ans = num_bottles;
+        
+        while num_bottles >= num_exchange {
+            num_bottles -= num_exchange;
+            num_exchange += 1;
+            ans += 1;
+            num_bottles += 1;
+        }
+        
+        ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->