docs: add Lucene.NET logo to the README

Minor enhancement with some branding

Author: jbampton

README.md

@@ -4,6 +4,8 @@
 [![Azure DevOps builds (master)](https://img.shields.io/azure-devops/build/lucene-net/6ba240c9-9598-47e7-a793-0ed8a4ba2f8b/3/master)](https://dev.azure.com/lucene-net/Lucene.NET/_build?definitionId=3&_a=summary)
 [![GitHub](https://img.shields.io/github/license/apache/lucenenet)](https://github.com/apache/lucenenet/blob/master/LICENSE.txt)
 
+[![Apache Lucene.NET Search Engine Library](branding/logo/lucene-net-color.png)](https://lucenenet.apache.org)
+
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