fix: update Package Overview github link (#262)

Author: alicejli

third_party/docfx-doclet-143274/src/main/java/com/google/docfx/doclet/RepoMetadata.java

@@ -149,6 +149,10 @@ public String getGithubLink() {
         || Objects.equals(this.repo, "googleapis/sdk-platform-java")) {
       githubLink = githubLink + "/tree/main/" + this.repoShort;
     }
+    // Handwritten libraries have a different base URI
+    else {
+      githubLink = githubLink + "/tree/main/";
+    }
     return githubLink;
   }