Add edit url (#501)

Author: recrwplay

preview.yml

@@ -7,6 +7,7 @@ content:
   sources:
   - url: ./
     branches: ['HEAD']
+    edit_url: https://github.com/neo4j/docs-cypher/tree/{refname}/{path}
     exclude:
     - '!**/_includes/*'
     - '!**/readme.adoc'