Add Linux build status badge to top of README (#440)

Summary:
Added a build status badge for Linux to the top of README.  It leaves the existing badge at the bottom under the "Build Status" header.

Pull Request resolved: #440

Reviewed By: AlnisM

Differential Revision: D102809472

Pulled By: pbhandar2

fbshipit-source-id: 33f4b5444cbdee242458a00850bfc85dc1f683d1

Author: rlyerly

README.md

@@ -2,6 +2,8 @@
   <img width="500" height="140" alt="CacheLib" src="website/static/img/CacheLib-Logo-Large-transp.png">
 </p>
 
+[![linux](https://github.com/facebook/CacheLib/actions/workflows/getdeps_linux.yml/badge.svg)](https://github.com/facebook/CacheLib/actions/workflows/getdeps_linux.yml)
+
 # CacheLib
 
 Pluggable caching engine to build and scale high performance cache services. See