Add contributed EBBR sequence files

It is convenient to have those sequence files at hand to analyse results
obtained with the different ACS-IR published versions.

Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>

README.md

@@ -326,3 +326,19 @@ their test run according to the log file.
 
 We create artificial tests entries for those dropped tests sets, with the
 "result" fields set to "SKIPPED".
+
+## Contributed files
+
+A few contributed files are stored in sub-folders under `contrib` for
+convenience:
+
+-------------------------------------------------------------------------------
+           Sub-folder  Contents
+---------------------  --------------------------------------------------------
+ `v21.05_0.8_BETA-0/`  EBBR sequence file from [ACS-IR v21.05_0.8_BETA-0].
+
+   `v21.07_0.9_BETA/`  EBBR sequence files from [ACS-IR v21.07_0.9_BETA].
+-------------------------------------------------------------------------------
+
+[ACS-IR v21.05_0.8_BETA-0]: https://github.com/ARM-software/arm-systemready/tree/main/IR/prebuilt_images/v21.05_0.8_BETA-0
+[ACS-IR v21.07_0.9_BETA]: https://github.com/ARM-software/arm-systemready/tree/main/IR/prebuilt_images/v21.07_0.9_BETA