Add testing docs in README

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>

README.md

@@ -43,6 +43,23 @@ If you do not with to build `runc` with seccomp support you can add `BUILDTAGS="
 | selinux   | selinux process and mount labeling | <none>      |
 | apparmor  | apparmor profile support           | libapparmor |
 
+### Testing:
+
+You can run tests for runC by using command:
+
+```bash
+# make test
+```
+
+Note that test cases are run in Docker container, so you need to install
+`docker` first. And test requires mounting cgroups inside container, it's
+done by docker now, so you need a docker version newer than 1.8.0-rc2.
+
+You can also run specific test cases by:
+
+```bash
+# make test TESTFLAGS="-run=SomeTestFunction"
+```
 
 ### Using: