README: Conditionally render dark/light mode logos depending on user's GitHub theme

Fixes: #1305
Co-authored-by: Saahil Ali <[email protected]>

Author: Onkar627

README.md

@@ -1,5 +1,5 @@
-![Logo](https://raw.githubusercontent.com/intel/dffml/master/docs/images/logo-lightmode.svg)
-
+![Logo-dark](https://raw.githubusercontent.com/intel/dffml/master/docs/images/logo-darkmode.svg#gh-dark-mode-only)
+![Logo-light](https://raw.githubusercontent.com/intel/dffml/master/docs/images/logo-lightmode.svg#gh-light-mode-only)
 [![Actions Status](https://github.com/intel/dffml/workflows/Tests/badge.svg?branch=master&event=push)](https://github.com/intel/dffml/actions)
 [![Gitpod Ready-to-Code](https://img.shields.io/badge/Gitpod-ready--to--code-blue?logo=gitpod)](https://gitpod.io/#https://github.com/intel/dffml)
 [![codecov](https://codecov.io/gh/intel/dffml/branch/master/graph/badge.svg)](https://codecov.io/gh/intel/dffml)