Add description url

Author: SaimMomin12

lib/galaxy/config/sample/datatypes_conf.xml.sample

@@ -597,7 +597,7 @@
     <datatype extension="odgi" type="galaxy.datatypes.binary:Binary" subclass="true" description="Genomic variation graphs self index used by odgi." display_in_upload="true"/>
     <datatype extension="vg" type="galaxy.datatypes.binary:CompressedArchive" subclass="true" description="Genomic variation graphs." display_in_upload="true"/>
     <datatype extension="xg" type="galaxy.datatypes.binary:Binary" subclass="true" description="Genomic variation graphs with vg index." display_in_upload="true"/>
-    <datatype extension="gam" type="galaxy.datatypes.binary:Binary" subclass="true" description="Binary file storing sequencing read alignments to genome variation graphs, used by the VG toolkit." display_in_upload="true"/>
+    <datatype extension="gam" type="galaxy.datatypes.binary:Binary" subclass="true" description="Binary file storing sequencing read alignments to genome variation graphs, used by the VG toolkit." display_in_upload="true" description_url="https://github.com/vgteam/vg/wiki/File-Formats#gam-graph-alignment--map-vgs-bam"/>
     <datatype extension="protobuf2" type="galaxy.datatypes.binary:Binary" subclass="true" description="Protocol Buffers (Protobuf) is data format for serializing structured data." display_in_upload="true"/>
     <datatype extension="protobuf3" type="galaxy.datatypes.binary:Binary" subclass="true" description="Protocol Buffers (Protobuf) is data format for serializing structured data." display_in_upload="true"/>
     <datatype extension="onnx" type="galaxy.datatypes.binary:Binary" subclass="true" description="ONNX (Open neural network exchange) is data format for storing and sharing machine learning and deep learning models." display_in_upload="true">