Add scala3doc logo and fix link

Author: romanowski

scala3doc/resources/dotty_res/images/scala3doc_logo.svg

@@ -145,6 +145,11 @@ th {
   margin-left: 42px;
   line-height: 42px;
 }
+
+.scala3doc_logo {
+  width: 116px;
+}
+
 .sideMenuPart {
   padding-left: 1em;
 }

scala3doc/resources/dotty_res/styles/scalastyle.css

@@ -303,9 +303,9 @@ class ScalaHtmlRenderer(ctx: DokkaContext) extends HtmlRenderer(ctx) {
                     raw(" Back to top")
                   )
                 ),
-                span(cls := "pull-right")(
-                  raw("Generated by "),
-                  a(href := "https://github.com/lampepfl/scala3doc")("Scala3doc")
+                raw("Generated by "),
+                a(href := "https://github.com/lampepfl/dotty/tree/master/scala3doc")(
+                  img(src := resolveRoot(page, "images/scala3doc_logo.svg"), alt := "Scala3doc", cls := "scala3doc_logo")
                 )
               )
             )

scala3doc/src/dotty/renderers/ScalaHtmlRenderer.scala

@@ -76,6 +76,7 @@ object HTML:
   val title = Tag("title")
   val body = Tag("body")
   val nav = Tag("nav")
+  val img = Tag("img")
 
   val cls = Attr("class")
   val href = Attr("href")
@@ -90,6 +91,7 @@ object HTML:
   val name = Attr("name")
   val content = Attr("content")
   val testId = Attr("data-test-id")
+  val alt = Attr("alt")
 
   def raw(content: String): AppliedTag = AppliedTag(content)