Add instructions for headerssync-params.py to release-process.md

Author: sipa

doc/release-process.md

@@ -43,6 +43,14 @@ Release Process
     - On mainnet, the selected value must not be orphaned, so it may be useful to set the height two blocks back from the tip.
     - Testnet should be set with a height some tens of thousands back from the tip, due to reorgs there.
   - `nMinimumChainWork` with the "chainwork" value of RPC `getblockheader` using the same height as that selected for the previous step.
+* Consider updating the headers synchronization tuning parameters to account for the chainparams updates.
+  The optimal values change very slowly, so this isn't strictly necessary every release, but doing so doesn't hurt.
+  - Update configuration variables in [`contrib/devtools/headerssync-params.py`](contrib/devtools/headerssync-params.py):
+    - Set `TIME` to the software's expected supported lifetime -- after this time, its ability to defend against a high bandwidth timewarp attacker will begin to degrade.
+    - Set `MINCHAINWORK_HEADERS` to the height used for the `nMinimumChainWork` calculation above.
+    - Check that the other variables still look reasonable.
+  - Run the script. It works fine in CPython, but PyPy is much faster (seconds instead of minutes): `pypy3 contrib/devtools/headerssync-params.py`.
+  - Paste the output defining `HEADER_COMMITMENT_PERIOD` and `REDOWNLOAD_BUFFER_SIZE` into the top of [`src/headerssync.cpp`](/src/headerssync.cpp).
 - Clear the release notes and move them to the wiki (see "Write the release notes" below).
 - Translations on Transifex:
     - Pull translations from Transifex into the master branch.