[MINOR] Add file encoding and file type for README.md
[MINOR] Add file encoding and file type for README.md

https://packaging.python.org/specifications/core-metadata/#description-content-type

Metadata:
Description-Content-Type: text/markdown;
charset=UTF-8;
variant=GFM

discussion: https://github.com/j143/systemds/issues/68

Closes  #1281.
apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml