Add the documentation for the PSR12 Import Statement sniff

Co-authored-by: Juliette <663378+jrfnl@users.noreply.github.com>

Author: dingo-d

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

@@ -0,0 +1,35 @@
+<documentation title="Import Statement">
+    <standard>
+    <![CDATA[
+    Import use statements must not begin with a leading backslash.
+    ]]>
+    </standard>
+    <code_comparison>
+        <code title="Valid: Import statement is fully qualified and doesn't begin with a leading backslash.">
+        <![CDATA[
+<?php
+
+use Vendor\Package\ClassA as A;
+
+class FooBar extends A
+{
+    use \FirstTrait;
+    use SecondTrait;
+}
+        ]]>
+        </code>
+        <code title="Invalid: Import statement begins with a leading backslash.">
+        <![CDATA[
+<?php
+
+use <em>\</em>Vendor\Package\ClassA as A;
+
+class FooBar extends A
+{
+    use \FirstTrait;
+    use SecondTrait;
+}
+        ]]>
+        </code>
+    </code_comparison>
+</documentation>