Fix userCmdRelayer signature in Gitbook Docs

[mshakeg]

It doesn't seem like the docs repo is public, so thought I'd create this issue here. The docs has a small function naming issue it should be userCmdRelayer not userCmdRouter as follows:

function userCmdRelayer (
  uint16 callpathIdx, 
  bytes cmd, 
  bytes conds,
  bytes tip,
  bytes signature)
  returns (bytes memory)