Add tests/README file

```Revision #1```  https://github.com/camelon/lizardfs/commit/00261fccd79e017cd219d7624a22440cfc7017ae
```Revision #2```  https://github.com/camelon/lizardfs/commit/19b31d2d839cc86cb4b494b6aea97483e9018fd6
```Revision #3```  https://github.com/camelon/lizardfs/commit/274dd3c19779241bced0ae7487b8dfcc2f905d3e (current)