Add headerssync-params.py script to the repository

contrib/devtools/README.md

@@ -90,6 +90,16 @@ example:
 BUILDDIR=$PWD/build contrib/devtools/gen-manpages.py
 ```
 
+headerssync-params.py
+=====================
+
+A script to generate optimal parameters for the headerssync module (src/headerssync.cpp). It takes no command-line
+options, as all its configuration is set at the top of the file. It runs many times faster inside PyPy. Invocation:
+
+```bash
+pypy3 contrib/devtools/headerssync-params.py
+```
+
 gen-bitcoin-conf.sh
 ===================