Add doc about running unit test

Author: SonicStark

docs/README.md

@@ -58,6 +58,10 @@ It introduces how our **MI** is built based on the previous **CLI** and its appl
 /python-bugzilla
 ](https://github.com/python-bugzilla/python-bugzilla), reading it will enable you to quickly understand and use this project.
 
+### `tests.md`
+
+Describe these things about running the unit test.
+
 ### `assets`: demos & charts
 
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