udated README.md

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diff --git a/tests/README.md b/tests/README.md
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+++ b/tests/README.md
@@ -6,6 +6,7 @@ This directory contains the following programs and scripts:
 - `frametest` : Test tool that checks lz4frame integrity on target platform
 - `fullbench`  : Precisely measure speed for each lz4 inner functions
 - `fuzzer`  : Test tool, to check lz4 integrity on target platform
+- `test-lz4-speed.py` : script for testing lz4 speed difference between commits
 - `test-lz4-versions.py` : compatibility test between lz4 versions stored on Github
 
 
@@ -16,6 +17,53 @@ Then all taged (released) versions of lz4 are compiled.
 In the following step interoperability between lz4 versions is checked.
 
 
+#### `test-lz4-speed.py` - script for testing lz4 speed difference between commits
+
+This script creates `speedTest` directory to which lz4 repository is cloned.
+Then it compiles all branches of lz4 and performs a speed benchmark for a given list of files (the `testFileNames` parameter).
+After `sleepTime` (an optional parameter, default 300 seconds) seconds the script checks repository for new commits.
+If a new commit is found it is compiled and a speed benchmark for this commit is performed.
+The results of the speed benchmark are compared to the previous results.
+If compression or decompression speed for one of lz4 levels is lower than `lowerLimit` (an optional parameter, default 0.98) the speed benchmark is restarted.
+If second results are also lower than `lowerLimit` the warning e-mail is send to recipients from the list (the `emails` parameter).
+
+Additional remarks:
+- To be sure that speed results are accurate the script should be run on a "stable" target system with no other jobs running in parallel
+- Using the script with virtual machines can lead to large variations of speed results
+- The speed benchmark is not performed until computers' load average is lower than `maxLoadAvg` (an optional parameter, default 0.75)
+- The script sends e-mails using `mutt`; if `mutt` is not available it sends e-mails without attachments using `mail`; if both are not available it only prints a warning
+
+
+The example usage with two test files, one e-mail address, and with an additional message:
+```
+./test-lz4-speed.py "silesia.tar calgary.tar" "email@gmail.com" --message "tested on my laptop" --sleepTime 60
+``` 
+
+To run the script in background please use:
+```
+nohup ./test-lz4-speed.py testFileNames emails &
+```
+
+The full list of parameters:
+```
+positional arguments:
+  testFileNames         file names list for speed benchmark
+  emails                list of e-mail addresses to send warnings
+
+optional arguments:
+  -h, --help            show this help message and exit
+  --message MESSAGE     attach an additional message to e-mail
+  --lowerLimit LOWERLIMIT
+                        send email if speed is lower than given limit
+  --maxLoadAvg MAXLOADAVG
+                        maximum load average to start testing
+  --lastCLevel LASTCLEVEL
+                        last compression level for testing
+  --sleepTime SLEEPTIME
+                        frequency of repository checking in seconds
+```
+
+
 #### License
 
 All files in this directory are licensed under GPL-v2.