[RFC PATCH v2 4/4] btrfs-progs: Add readme for export testsuits

[Gu Jinxiang <gujx@cn.fujitsu.com>]

Add the readme of command for export testsuits.
And add the excute method of exported testsuits.

Signed-off-by: Gu Jinxiang <gujx@cn.fujitsu.com>
---
 tests/README.md | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tests/README.md b/tests/README.md
index 04d2ce2a..9f4c01ac 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -48,6 +48,26 @@ $ TEST=001\* ./fsck-tests.sh
 will run the first test in fsck-tests subdirectory.
 
 
+## Package testsuit
+
+The tests can be export as a tests.tar.gz into path given. Use:
+
+```shell
+$ make EXPORT=PATH package
+```
+
+where `PATH` is a directory where tests.tar.gz be genereated.
+Here comes handy:
+
+```shell
+$ make EXPORT=/home/user/ package
+$ make EXPORT=../../dir/ package
+```
+
+And, after decompress tests.tar.gz, test can be run selectively
+from `tests/` directory introduced above.
+
+
 ## Test structure
 
 *tests/fsck-tests/:*
-- 
2.14.3