fix: Add config doc for expire_results

config/generic.json.sample

@@ -25,6 +25,7 @@
         "concurrent_captures": "How many captures can happen at the same (expect ~2Gb of ram/capture)",
         "only_global_lookups": "Set it to True if your instance is publicly available so users aren't able to scan your internal network",
         "max_capture_time": "The very maximal time we allow a capture to keep going. Should only be triggered by captures that cause playwright to never quit, or captures with way too many children.",
+        "expire_results": "The capture results are stored in redis. The time after which they're expired (in seconds). Set it to a lower value (but not too low) if you have a lot of captures and not a lot of memory",
         "max_retries": "The very maximal amount of times lacus will retry a failing capture.",
         "tor_proxy": "URL to connect to a SOCKS 5 proxy for tor",
         "global_proxy": "Proxy configuration to use for *all* the requests (except .onions)"