Provide links to used classes from PHP code example

Author: lalshe

README.md

@@ -13,6 +13,11 @@ It is strictly advised to use any form of DI container (e.g. [Symfony Bundle](ht
 ```php
 <?php
 
+use Jaeger\Tag\StringTag;
+use Jaeger\Tracer\TracerInterface;
+
+/** @var TracerInterface $tracer */
+
 $span = $tracer->start('Parent Operation Name', [new StringTag('test.tag', 'Hello world in parent')]);
 $childSpan = $tracer->start('Child Operation Name', [new StringTag('test.tag', 'Hello world in child')]);
 $tracer->finish($childSpan);