Add description and metdatada to shard.yml (#662)

Co-authored-by: Julien Portalier <[email protected]>

shard.yml

@@ -1,9 +1,15 @@
 name: shards
 version: 0.18.0
+description: |
+ Resolves, installs and updates project dependencies reproducibly from source
+ repositories.
 
 authors:
   - Julien Portalier <[email protected]>
 
+documentation: https://crystal-lang.org/reference/man/shards
+repository: https://github.com/crystal-lang/shards
+
 dependencies:
   molinillo:
     github: crystal-lang/crystal-molinillo