Add some meta alternate links (#2657)

src/server/web/views/note.pug

@@ -23,3 +23,6 @@ block meta
 		link(rel='prev' href=`${config.url}/notes/${note.prev}`)
 	if note.next
 		link(rel='next' href=`${config.url}/notes/${note.next}`)
+
+	if !user.host
+		link(rel='alternate' href=url type='application/activity+json')

src/server/web/views/user.pug

@@ -18,3 +18,10 @@ block meta
 	meta(property='og:description' content= user.description)
 	meta(property='og:url'         content= url)
 	meta(property='og:image'       content= img)
+	
+	if !user.host
+		link(rel='alternate' href=`${config.url}/users/${user._id}` type='application/activity+json')
+	if user.uri
+		link(rel='alternate' href=user.uri type='application/activity+json')
+	if user.url
+		link(rel='alternate' href=user.url type='text/html')