ci: upload unit test coverage file to codecov.io (#22)

diff --git a/.github/workflows/runner-test.yml b/.github/workflows/runner-test.yml
index c3ec9eb..af36bef 100644
--- a/.github/workflows/runner-test.yml
+++ b/.github/workflows/runner-test.yml
@@ -46,3 +46,6 @@
         run: make setup install
       - name: Run unit tests
         run: make test
+      - name: Upload coverage profile
+        if: ${{ matrix.python-version == '3.6' }}
+        run: bash <(curl -s https://codecov.io/bash)
diff --git a/README.md b/README.md
index accdcfe..3d7525d 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,7 @@
 [![Runner Unit Test](https://github.com/apache/apisix-python-plugin-runner/actions/workflows/runner-test.yml/badge.svg?branch=master)](https://github.com/apache/apisix-python-plugin-runner/actions)
 [![Runner Lint Checker](https://github.com/apache/apisix-python-plugin-runner/actions/workflows/runner-lint.yml/badge.svg?branch=master)](https://github.com/apache/apisix-python-plugin-runner/actions)
 [![Runner License Checker](https://github.com/apache/apisix-python-plugin-runner/actions/workflows/runner-license.yml/badge.svg?branch=master)](https://github.com/apache/apisix-python-plugin-runner/actions)
+[![Codecov](https://codecov.io/gh/apache/apisix-python-plugin-runner/branch/master/graph/badge.svg)](https://codecov.io/gh/apache/apisix-python-plugin-runner)
 
 Runs [Apache APISIX](http://apisix.apache.org/) plugins written in Python. Implemented as a sidecar that accompanies
 APISIX.