README: update CI status URL, badge, test program

Update URLs to CI status, badge, update programming language of
test programs.

README.md

@@ -1,7 +1,7 @@
 # update-ssh-keys
 
-[![Build Status](https://travis-ci.org/coreos/update-ssh-keys.svg?branch=master)](https://travis-ci.org/coreos/update-ssh-keys)
-![minimum rust 1.28](https://img.shields.io/badge/rust-1.28%2B-orange.svg)
+[![Github CI](https://github.com/flatcar/update-ssh-keys/actions/workflows/rust.yml/badge.svg)](https://github.com/flatcar/update-ssh-keys/actions)
+![minimum rust 1.60](https://img.shields.io/badge/rust-1.60%2B-orange.svg)
 
 `update-ssh-keys` is a command line tool and a library for managing openssh
 authorized public keys. It keeps track of sets of keys with names, allows for
@@ -15,6 +15,6 @@ non-Container Linux machine, you can build the project with `cargo build
 --release`. The rust toolchain is required to build it. You can install `rustup`
 to manage your rust toolchain - https://www.rustup.rs. 
 
-`test/test_update_ssh_keys.py` is a python script which tests the functionality
+`test/test_update_ssh_keys.rs` is a Rust program which tests the functionality
 of the `update-ssh-keys` command line tool. If changes are made to
 `update-ssh-keys`, that script should be run.