Link to wiki for changeset comments

Added the link:http://wiki.openstreetmap.org/wiki/Good_changeset_comments
below the comment box

Issue: openstreetmap#2923

data/core.yaml

@@ -203,6 +203,8 @@ en:
     modified: Modified
     deleted: Deleted
     created: Created
+    about_changeset_comments: About changeset comments
+    about_changeset_comments_link: //wiki.openstreetmap.org/wiki/Good_changeset_comments
   contributors:
     list: "Edits by {users}"
     truncated_list: "Edits by {users} and {count} others"
@@ -760,4 +762,3 @@ en:
       help: "You can replay this walkthrough or view more documentation by clicking the {button} Help button."
       save: "Don't forget to regularly save your changes!"
       start: "Start mapping!"
-

js/id/ui/commit.js

@@ -68,6 +68,17 @@ iD.ui.Commit = function(context) {
             commentField.call(d3.combobox().data(comments));
         });
 
+        var changeSetInfo = commentSection.append('div')
+            .attr('class', 'changeset-info');
+
+        changeSetInfo.append('a')
+          .attr('target', '_blank')
+          .attr('tabindex', -1)
+          .call(iD.svg.Icon('#icon-out-link', 'inline'))
+          .attr('href', t('commit.about_changeset_comments_link'))
+          .append('span')
+          .text(t('commit.about_changeset_comments'));
+
         // Warnings
         var warnings = body.selectAll('div.warning-section')
             .data([context.history().validate(changes)])