Update intro with link to explorer application (#93)

* update intro with link to web app

* fix broken link causing tests to fail

Author: HuwCheston

mirdotcom/content/2_music_representations/sheet_music_representations.ipynb

@@ -204,7 +204,7 @@
    },
    "source": [
     "ipd.Image(\n",
-    "    url=\"https://upload.wikimedia.org/wikipedia/commons/thumb/9/98/Pitch_class_on_C.png/187px-Pitch_class_on_C.png\"\n",
+    "    url=\"https://upload.wikimedia.org/wikipedia/commons/0/03/Middle_C.png\"\n",
     ")"
    ],
    "outputs": [

mirdotcom/intro.md

@@ -2,10 +2,13 @@
 
 This repository contains instructional notebooks related to music information retrieval (MIR). Inside these notebooks are Python code snippets that illustrate basic MIR systems.
 
+> **New to Music Information Retrieval?** Try out our [web application](https://explorer.musicinformationretrieval.com) to get hands-on experience exploring music recordings with AI tools!
+
 ## Updates
 
+- 2026 March 25: We're excited to announce a new web application designed for *exploring music recordings and audio files with machine learning tools*. You can access it **for free** at [explorer.musicinformationretrieval.com](https://explorer.musicinformationretrieval.com).
 - 2025 October 31: As part of our efforts to modernise this site, we'd welcome additional tutorials and notebooks (in `.ipynb` format) to feature on this site. Please [submit a pull request](https://help.github.com/articles/using-pull-requests) on the repository.
-- 2025 October 22: Hey! I'm [Huw Cheston](https://huwcheston.github.io) and I'm excited to be working with Iran on modernising this site as part of the [EPSRC](https://www.ukri.org/councils/epsrc/) "AI Skills Through Music" project. I completed my PhD in MIR at the [University of Cambridge](https://cms.mus.cam.ac.uk/) and now work at the [Centre for Digital Music, Queen Mary University](https://www.c4dm.eecs.qmul.ac.uk/). Feel free to reach out and say hi! `h \<dot\> cheston \<at\> qmul \<dot\> ac \<dot\> uk`.
+- 2025 October 22: Hey! I'm [Huw Cheston](https://huwcheston.github.io) and I'm excited to be working with Iran on modernising this site as part of the [EPSRC](https://www.ukri.org/councils/epsrc/) "AI Skills Through Music" project. I completed my PhD in MIR at the [University of Cambridge](https://cms.mus.cam.ac.uk/) and now work at the [Centre for Digital Music, Queen Mary University](https://www.c4dm.eecs.qmul.ac.uk/). Feel free to [email me](mailto:huw@musicinformationretrieval.com) and say hi!
 - 2023 October 09: Hello everyone! I'm [Iran R. Roman](https://iranroman.github.io) and I'm honored to be [the new administrator](https://iranroman.github.io/2023/10/09/other-list-01.html) of [musicinformationretrieval.com](https://musicinformationretrieval.com). Feel free to reach out and say hi. I would love to hear from you. iran \<at\> ccrma \<dot\> stanford \<dot\> edu
 
 ## Contributions