contrib: make DNS seeds file an argument in CLI

contrib/seeds/README.md

@@ -13,6 +13,6 @@ data. Run the following commands from the `/contrib/seeds` directory:
 
     curl https://bitcoin.sipa.be/seeds.txt.gz | gzip -dc > seeds_main.txt
     curl https://bitcoin.sipa.be/asmap-filled.dat > asmap-filled.dat
-    python3 makeseeds.py -a asmap-filled.dat < seeds_main.txt > nodes_main.txt
+    python3 makeseeds.py -a asmap-filled.dat -s seeds_main.txt > nodes_main.txt
     cat nodes_main_manual.txt >> nodes_main.txt
     python3 generate-seeds.py . > ../../src/chainparamsseeds.h