Add OpenBSDĀ® to the list of supported systems

Resolves COMPMID-5396

Change-Id: I9bf296b81145c48aabdfb56b7ffdb453f5a76976
Signed-off-by: Pablo Marquez Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/7892
Benchmark: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michalis Spyrou <michalis.spyrou@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/README.md b/README.md
index f780252..328a754 100644
--- a/README.md
+++ b/README.md
@@ -91,6 +91,7 @@
 - Android™
 - Bare Metal
 - Linux®
+- OpenBSD®
 - macOS®
 - Tizen™