added other recommendations

Author: Toby Hodges

_episodes/20-software-requirements.md

@@ -45,12 +45,15 @@ given in the form of an [RRID][rrid]. Resources with RRIDs can be looked up in t
 [SciCrunch][scicrunch] registry, which provides a portal for finding, tracking,
 and referring to scientific resources consistently. If you want to specify a
 tool as a `SoftwareRequirement`, search for the tool on SciCrunch and use the
-RRID that it has been assigned in the registry. You can use this RRID to refer
+RRID that it has been assigned in the registry. (Follow [this tutorial][scicrunch-add-tool]
+if you want to add a tool to SciCrunch.) You can use this RRID to refer
 to the tool (via [identifiers.org][identifiers]) in the `specs` field of your
-requirement description.
+requirement description. Other good choices, in order of preference, are to
+include the DOI for the main tool citation and the URL to the tool.
 
 
 [rrid]: https://scicrunch.org/resources/about/resource
 [scicrunch]: https://scicrunch.org/
 [dependencies]: https://github.com/common-workflow-language/cwltool#leveraging-softwarerequirements-beta
 [identifiers]: https://identifiers.org/
+[scicrunch-add-tool]: https://scicrunch.org/page/tutorials/336