Update Python version in documentation

The Python requirement has been relaxed to 3.7+.

Change-Id: Ibee4a31af0b5a458163cfcd428d8ca0b8018e79e
diff --git a/README.md b/README.md
index 1efefec..f7ba476 100644
--- a/README.md
+++ b/README.md
@@ -22,10 +22,10 @@
 ## Building
 
 Building core platform requires a recent version of CMake, a C/C++ cross compiler
-for Arm Cortex-M and Python 3.8+. There are sample toolchain files provided for
+for Arm Cortex-M and Python 3.7+. There are sample toolchain files provided for
 Arm Clang and Arm GCC.
 
-To run the helper scripts Python 3.8+ is required, together with the packages listed in
+To run the helper scripts Python 3.7+ is required, together with the packages listed in
 `requirements.txt`.
 
 ```