README: add references to RPM support (#160)

Signed-off-by: Valentin Rothberg <[email protected]>

Author: vrothberg

README.md

@@ -9,6 +9,7 @@ container-diff is a tool for analyzing and comparing container images. container
 - Docker Image History
 - Image file system
 - Apt packages
+- RPM packages
 - pip packages
 - npm packages
 These analyses can be performed on a single image, or a diff can be performed on two images to compare. The tool can help users better understand what is changing inside their images, and give them a better look at what their images contain.
@@ -43,6 +44,7 @@ To use `container-diff analyze` to perform analysis on a single image, you need
 container-diff analyze <img>     [Run default analyzers]
 container-diff analyze <img> --type=history  [History]
 container-diff analyze <img> --type=file  [File System]
+container-diff analyze <img> --type=rpm  [RPM]
 container-diff analyze <img> --type=pip  [Pip]
 container-diff analyze <img> --type=apt  [Apt]
 container-diff analyze <img> --type=node  [Node]
@@ -57,6 +59,7 @@ To use container-diff to perform a diff analysis on two images, you need two Doc
 container-diff diff <img1> <img2>     [Run default differs]
 container-diff diff <img1> <img2> --type=history  [History]
 container-diff diff <img1> <img2> --type=file  [File System]
+container-diff diff <img1> <img2> --type=rpm  [RPM]
 container-diff diff <img1> <img2> --type=pip  [Pip]
 container-diff diff <img1> <img2> --type=apt  [Apt]
 container-diff diff <img1> <img2> --type=node  [Node]