Add the documentation for the PSR12 Import Statement sniff

Author: dingo-d

src/Standards/PSR12/Docs/Files/ImportStatementStandard.xml

@@ -0,0 +1,55 @@
+<documentation title="Import Statement">
+    <standard>
+    <![CDATA[
+    Import statements must not begin with a leading backslash.
+    ]]>
+    </standard>
+    <code_comparison>
+        <code title="Valid: Import statements are fully qualified and don't begin a leading backslash.">
+        <![CDATA[
+<?php
+
+/**
+ * This is a file comment.
+ */
+
+declare(strict_types=1);
+
+namespace Vendor\Package;
+
+use Vendor\Package\{ClassA as A, ClassB};
+
+/**
+ * FooBar is an example class.
+ */
+class FooBar
+{
+    // ... additional PHP code ...
+}
+        ]]>
+        </code>
+        <code title="Invalid: Import statements begin with a leading backslash.">
+        <![CDATA[
+<?php
+
+/**
+ * This is a file comment.
+ */
+
+declare(strict_types=1);
+
+namespace Vendor\Package;
+
+use <em>\</em>Vendor\Package\{ClassA as A, ClassB};
+
+/**
+ * FooBar is an example class.
+ */
+class FooBar
+{
+    // ... additional PHP code ...
+}
+        ]]>
+        </code>
+    </code_comparison>
+</documentation>