docs: add koko eating bananas problem description

Author: bujosa

src/medium/readme.md

@@ -693,3 +693,39 @@ Put the code below in main.rs and run `cargo run`
   let result = medium::car_fleet::car_fleet(target, position, speed);
   println!("result: {}", result);
 ```
+
+# 875. Koko Eating Bananas
+
+## Description
+
+Koko loves to eat bananas. There are n piles of bananas, the ith pile has piles[i] bananas. The guards have gone and will come back in h hours.
+
+Koko can decide her bananas-per-hour eating speed of k. Each hour, she chooses some pile of bananas and eats k bananas from that pile. If the pile has less than k bananas, she eats all of them instead and will not eat any more bananas during this hour.
+
+Koko likes to eat slowly but still wants to finish eating all the bananas before the guards return.
+
+Return the minimum integer k such that she can eat all the bananas within h hours.
+
+## Examples
+
+```text
+Input: piles = [3,6,7,11], h = 8
+Output: 4
+
+Input: piles = [30,11,23,4,20], h = 5
+Output: 30
+
+Input: piles = [30,11,23,4,20], h = 6
+Output: 23
+```
+
+## How to Run in main.rs
+
+Put the code below in main.rs and run `cargo run`
+
+```rust
+  let piles = vec![3, 6, 7, 11];
+  let h = 8;
+  let result = medium::min_eating_speed::min_eating_speed(piles, h);
+  println!("result: {}", result);
+```