feat: add php solution to lc problem: No.0028 (doocs#912)

No.0028.Find the Index of the First Occurrence in a String

Author: Qiu-IT

Diff for: solution/0000-0099/0028.Find the Index of the First Occurrence in a String/README.md

@@ -345,6 +345,31 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param String $haystack
+     * @param String $needle
+     * @return Integer
+     */
+    function strStr($haystack, $needle) {
+        $strNew = str_replace($needle, "+", $haystack);
+        $cnt = substr_count($strNew, "+");
+        if ($cnt > 0) {
+            for ($i = 0; $i < strlen($strNew); $i++) {
+                if ($strNew[$i] == "+") {
+                    return $i;
+                }
+            }
+        } else {
+            return -1;
+        }
+    }
+}
+```
+
 ### **...**
 
 ```

Diff for: solution/0000-0099/0028.Find the Index of the First Occurrence in a String/README_EN.md

@@ -331,6 +331,31 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param String $haystack
+     * @param String $needle
+     * @return Integer
+     */
+    function strStr($haystack, $needle) {
+        $strNew = str_replace($needle, "+", $haystack);
+        $cnt = substr_count($strNew, "+");
+        if ($cnt > 0) {
+            for ($i = 0; $i < strlen($strNew); $i++) {
+                if ($strNew[$i] == "+") {
+                    return $i;
+                }
+            }
+        } else {
+            return -1;
+        }
+    }
+}
+```
+
 ### **...**
 
 ```

Diff for: solution/0000-0099/0028.Find the Index of the First Occurrence in a String/Solution.php

@@ -0,0 +1,20 @@
+class Solution {
+    /**
+     * @param String $haystack
+     * @param String $needle
+     * @return Integer
+     */
+    function strStr($haystack, $needle) {
+        $strNew = str_replace($needle, "+", $haystack);
+        $cnt = substr_count($strNew, "+");
+        if ($cnt > 0) {
+            for ($i = 0; $i < strlen($strNew); $i++) {
+                if ($strNew[$i] == "+") {
+                    return $i;
+                }
+            }
+        } else {
+            return -1;
+        }
+    }
+}