Adding the str_before helper to the docs

Author: afsardo

helpers.md

@@ -78,6 +78,7 @@ Laravel includes a variety of global "helper" PHP functions. Many of these funct
 [str_limit](#method-str-limit)
 [starts_with](#method-starts-with)
 [str_after](#method-str-after)
+[str_before](#method-str-before)
 [str_contains](#method-str-contains)
 [str_finish](#method-str-finish)
 [str_is](#method-str-is)
@@ -606,6 +607,14 @@ The `str_after` function returns everything after the given value in a string:
 
     // ' a test'
 
+<a name="method-str-before"></a>
+#### `str_before()` {#collection-method}
+
+The `str_before` function returns everything before the given value in a string:
+
+    $value = str_before('Test :it before', ':it before');
+
+    // 'Test '
 
 <a name="method-str-contains"></a>
 #### `str_contains()` {#collection-method}