add unit test doc

docs/index.rst

@@ -44,6 +44,7 @@ Userful links:
    run_tab
    udapp
    contract_metadata
+   unittesting_tab
 
 .. toctree::
    :maxdepth: 2

docs/unittesting_tab.md

@@ -0,0 +1,24 @@
+Unit Testing
+============
+
+The unit testing tab allows to run unit testing.
+
+![image](images/remix_unittest.png)
+
+Generate test File
+------------------
+
+This create a new solidity file in the current folder suffixed with `_test`.
+This file contains the minimun you need for running unit testing.
+
+Run Tests
+---------
+
+This execute tests. The execution is run in a separate environment and the result is displayed below.
+
+Continuous integration
+----------------------
+
+remix-tests is also a CLI, it can be used in a continuous integration environement which support node.js.
+Please find more information
+https://github.com/ethereum/remix/tree/master/remix-tests