devtools: Update README.md

Author: MarcoFalke

contrib/devtools/README.md

@@ -62,6 +62,11 @@ optimize-pngs.py
 A script to optimize png files in the bitcoin
 repository (requires pngcrush).
 
+security-check.py and test-security-check.py
+============================================
+
+Perform basic ELF security checks on a series of executables.
+
 symbol-check.py
 ===============