[misc] Improve README

Changes `--enable-file-urls` description to correct file URI schema

README.md

@@ -410,7 +410,7 @@ If you fork the project on GitHub, you can run your fork's [build workflow](.git
     --list-impersonate-targets      List available clients to impersonate.
     -4, --force-ipv4                Make all connections via IPv4
     -6, --force-ipv6                Make all connections via IPv6
-    --enable-file-urls              Enable file:// URLs. This is disabled by
+    --enable-file-urls              Enable file:/// URLs. This is disabled by
                                     default for security reasons.
 
 ## Geo-restriction: