feat: add php solution to lc problem: No.0509 (doocs#919)

No.0509.Fibonacci Number

Author: Qiu-IT

solution/0500-0599/0509.Fibonacci Number/README.md

@@ -184,6 +184,27 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function fib($n) {
+        if ($n == 0 || $n == 1) {
+            return $n;
+        }
+        $dp = [0, 1];
+        for ($i = 2; $i <= $n; $i++) {
+            $dp[$i] = $dp[$i - 2] + $dp[$i - 1];
+        }
+        return $dp[$n];
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0500-0599/0509.Fibonacci Number/README_EN.md

@@ -174,6 +174,27 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function fib($n) {
+        if ($n == 0 || $n == 1) {
+            return $n;
+        }
+        $dp = [0, 1];
+        for ($i = 2; $i <= $n; $i++) {
+            $dp[$i] = $dp[$i - 2] + $dp[$i - 1];
+        }
+        return $dp[$n];
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0500-0599/0509.Fibonacci Number/Solution.php

@@ -0,0 +1,16 @@
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function fib($n) {
+        if ($n == 0 || $n == 1) {
+            return $n;
+        }
+        $dp = [0, 1];
+        for ($i = 2; $i <= $n; $i++) {
+            $dp[$i] = $dp[$i - 2] + $dp[$i - 1];
+        }
+        return $dp[$n];
+    }
+}