added new logo

The logo was created by the Kali Linux team and gave us permission to
use it.

In addition to the new logo, the ./images/ directory has been
moved to into ./docs/ in order to make the root directory of the project
cleaner. The old preview.png was never used as we had been using a
preview image that was hosted on user-images.githubuesrcontent.com. This
too has been changed so that we use the local copy instead

Author: sdushantha

docs/README.md

@@ -1,6 +1,6 @@
 <p align=center>
   <br>
-  <a href="https://sherlock-project.github.io/" target="_blank"><img src="https://user-images.githubusercontent.com/27065646/53551960-ae4dff80-3b3a-11e9-9075-cef786c69364.png"/></a>
+  <a href="https://sherlock-project.github.io/" target="_blank"><img src="images/sherlock-logo.png"/></a>
   <br>
   <span>Hunt down social media accounts by username across <a href="https://github.com/sherlock-project/sherlock/blob/master/docs/sites.md">400+ social networks</a></span>
   <br>
@@ -17,7 +17,7 @@
 </p>
 
 <p align="center">
-<img width="70%" height="70%" src="https://user-images.githubusercontent.com/27065646/219638267-a5e11090-aa6e-4e77-87f7-0e95f6ad5978.png"/>
+<img width="70%" height="70%" src="images/preview.png"/>
 </a>
 </p>