Increase default CONCURRENCY for replicator (#1550)

Since most users seem to connect to a remote hub, increase the default
concurrency.

apps/replicator/README.md

@@ -30,8 +30,12 @@ Once the Docker images have finished downloading, you should start to see messag
 ...
 ```
 
+If you are connected to a hub over the internet (rather than on the same machine or private network) the increased latency will make this take longer, and you will likely need to wait some time before an estimation of the time remaining will appear. This is expected.
+
 You may see messages out of order—this is fine. If messages like above are appearing, replication is working as expected.
 
+Note that the number of messages in the Postgres table will **not** match the number in the hub, because the replicator doesn't backfill "Remove" messages (like `CastRemove` and `ReactionRemove`) since these technically indicate an absence of content, not the presence.
+
 ### Connecting to Postgres
 
 While it will take a few hours to fully sync all data from the hub, you can start to query data right away.

scripts/replicator.sh

@@ -170,7 +170,8 @@ write_env_file() {
     fi
 
     if ! key_exists "CONCURRENCY"; then
-        echo "CONCURRENCY=$(portable_nproc)" >> .env
+        echo "# Set this higher the further the hub is from the replicator"
+        echo "CONCURRENCY=$(expr 4 \* $(portable_nproc))" >> .env
     fi
 
     if ! key_exists "WORKER_TYPE"; then