Improve Crosswalk page introduction and contribution instructions

Author: meldra

content/crosswalk/_index.md

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 title: "Crosswalks"
-#layout: single
+layout: list
 ---
 
-The CodeMeta crosswalk provides an explicit map between the metadata fields used by a broad range of software repositories, registries and archives.  Here are the currently available mappings from existing standards into CodeMeta properties.  Mapping onto a common set of properties should facilitate translation between any two crosswalked standards.  The full crosswalk table is [available as a `.csv`](https://github.com/codemeta/codemeta/tree/master/crosswalk.csv) file on the CodeMeta repository.  
+CodeMeta Crosswalks provide an explicit map between the fields of existing
+metadata standards, as used by a broad range of software repositories, 
+registries, and archives. When mapped by a Crosswalk, CodeMeta's terms act as
+a common set of properties, providing a pathway for metadata to be translated
+between standards.
 
-## Contribute!
+Crosswalks are not required to have a one-to-one mapping for every field.
+Because Crosswalks only map fields common between a standard and CodeMeta, the
+subset of common fields may differ a lot between Crosswalks. The diagram below
+demonstrates how CodeMeta maps between standards when there are differences.
 
-CodeMeta encourages submissions of additional vocabularies by making Pull Requests against the [full crosswalk table](https://github.com/codemeta/codemeta/tree/master/crosswalk.csv).  Feel free to propose corrections or extensions in the [CodeMeta issues tracker](https://github.com/codemeta/codemeta/issues).
+![Diagram of CodeMeta mapping between two metadata standards. It shows a common term, terms unique to each standard, and terms common to only CodeMeta and each standard.](/img/crosswalkdiagram.svg)
+
+### Contribute!
+
+CodeMeta encourages submissions of additional vocabularies. Refer to the
+[CodeMeta repository contribution guide](https://github.com/codemeta/codemeta?tab=contributing-ov-file#contributing-a-new-mapping)
+to submit a new Crosswalks.
+
+Crosswalks are not automatically listed on this website.
+[The guide for contributing to this website](https://github.com/codemeta/codemeta.github.io?tab=contributing-ov-file#adding-new-crosswalks)
+explains how to set that up.
+
+Please feel welcome to propose corrections or extensions in the [CodeMeta issues tracker](https://github.com/codemeta/codemeta/issues).
+
+## Crosswalk directory
+
+This directory contains many of the available Crosswalks. The full Crosswalk table is
+[available as a `.csv`](https://github.com/codemeta/codemeta/tree/master/crosswalk.csv)
+file in the CodeMeta repository.