feat(0344-reverse-string): add py3 solution

0344_reverse-string/python3/solution.py

@@ -0,0 +1,13 @@
+class Solution:
+    def reverseString(self, s: List[str]) -> None:
+        """
+        Do not return anything, modify s in-place instead.
+        """
+        i = 0
+        j = len(s) - 1
+        
+        while i < j:
+            s[i], s[j] = s[j], s[i]
+            i += 1
+            j -= 1
+