README.md,requirements.txt: add missing construct version info

Change-Id: I90da0df431f0d7dbfa4aa428366fbf0e35db388f
Related: OS#5666
diff --git a/requirements.txt b/requirements.txt
index 320cc7a..4f037da 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,7 +3,7 @@
 pytlv
 cmd2==1.5
 jsonpath-ng
-construct
+construct>=2.9.51
 bidict
 gsm0338
 pyyaml>=5.1