feat: add specs for min window

Author: bujosa

src/hard/minimum_window_substring.rs

@@ -0,0 +1,16 @@
+#![allow(dead_code)]
+pub fn min_window(s: String, t: String) -> String {
+    "".to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_min_window() {
+        let s = "ADOBECODEBANC".to_string();
+        let t = "ABC".to_string();
+        assert_eq!(min_window(s, t), "BANC".to_string());
+    }
+}