model_summary.md - Restore link to Harvard's Annotated Transformer.
Author: gamepad-coder
Pull request: yes

# What does this PR do?

**Why:**
- Action item from conversation here: <br> https://github.com/huggingface/transformers/pull/21408#issuecomment-1988788868

**What**
- Single parenthetical added <br>to the first sentence of the intro paragraph under the **The Transformer model family** header (just after the link to the original Transformer paper).
- Restores a link to Harvard's iconic "The Annotated Transformer" <br> http://nlp.seas.harvard.edu/2018/04/03/attention.html
- (See before and after mockup @ bottom of this PR description)

**Page updated**
- https://huggingface.co/docs/transformers/model_summary

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @pacman100

Integrations:

- deepspeed: HF Trainer/Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc and @younesbelkada

Documentation: @stevhliu and @MKhalusova

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
- TensorFlow: @Rocketknight1

 -->

<br><br>

----

**=== Mockup using DevTools in Chrome ===**

Before PR (current `main` on left)
After PR (this branch on right)

![chrome_WwbmQjiTYz](https://github.com/huggingface/transformers/assets/65138515/f0e5f13d-afa2-436a-b7a8-397ea8235d88)

https://huggingface.co/docs/transformers/model_summary

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_29702). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.