fix: add alt tag to contributors img

Author: othneildrew

BLANK_README.md

@@ -184,7 +184,7 @@ Don't forget to give the project a star! Thanks again!
 ### Top contributors:
 
 <a href="https://github.com/github_username/repo_name/graphs/contributors">
-  <img src="https://contrib.rocks/image?repo=github_username/repo_name" />
+  <img src="https://contrib.rocks/image?repo=github_username/repo_name" alt="contrib.rocks image" />
 </a>
 
 

README.md

@@ -198,7 +198,7 @@ Don't forget to give the project a star! Thanks again!
 ### Top contributors:
 
 <a href="https://github.com/othneildrew/Best-README-Template/graphs/contributors">
-  <img src="https://contrib.rocks/image?repo=othneildrew/Best-README-Template" />
+  <img src="https://contrib.rocks/image?repo=othneildrew/Best-README-Template" alt="contrib.rocks image" />
 </a>
 
 <p style="text-align: right;">(<a href="#readme-top">back to top</a>)</p>