Update to README.md

Updated README.md to add more information about the new `womtool` validation.

Author: jonn-smith

README.md

@@ -43,6 +43,8 @@ requires `column`, `curl`, `mail`, and [jq](https://stedolan.github.io/jq/)
    * `submit` `[-w]` *`<wdl>`* *`<inputs_json>`* `[options_json]` `[included_wdl_zip_file]`
      * Submit a new workflow.
      * Will automatically validate the WDL and JSON file if `womtool` is in your path.
+       * To add `womtool` to your path, install `cromwell` with brew:
+         * `brew install cromwell`
      * *`-w`*                     Wait for workflow to transition from 'Submitted' to some other status
                                   before ${SCRIPTNAME} exits
      * *`included_wdl_zip_file`*  Zip file containing any WDL files included in the input WDL