?DOCS? Added singularity badge to the Readme.

Author: hansendx

README.md

@@ -1,9 +1,11 @@
 # singularity-r
+[![https://www.singularity-hub.org/static/img/hosted-singularity--hub-%23e32929.svg](https://www.singularity-hub.org/static/img/hosted-singularity--hub-%23e32929.svg)](https://singularity-hub.org/collections/623)
+
 Singularity recipes for base-images containing R.
 
  * R is installed from source which is downloaded from [CRAN](https://cran.r-project.org/) (Comprehensive R Archive Network).
  * Packages needed to build R and those needed to run R like gfortran, g++ and gcc are installed through the debian repositories via `apt-get install`.
  * At the end of the build process the images is cleaned up by:
     * removing packages only needed for the build,
     * removing the package cache,
-    * removing downloaded files used for the build.
+    * removing downloaded files used for the build.