Add mdformat to precommit checks and update other version (#7529)

* Update .pre-commit-config.yaml

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update .pre-commit-config.yaml

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update CONTRIBUTING.md

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update README.md

* Update README.md

* Update README.md

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

CONTRIBUTING.md

@@ -18,16 +18,19 @@ Submitting a PR is easy! This example shows how to submit a PR for updating `req
 ### 1. Select File to Update
 
 Select `requirements.txt` to update by clicking on it in GitHub.
+
 <p align="center"><img width="800" alt="PR_step1" src="https://user-images.githubusercontent.com/26833433/122260847-08be2600-ced4-11eb-828b-8287ace4136c.png"></p>
 
 ### 2. Click 'Edit this file'
 
 Button is in top-right corner.
+
 <p align="center"><img width="800" alt="PR_step2" src="https://user-images.githubusercontent.com/26833433/122260844-06f46280-ced4-11eb-9eec-b8a24be519ca.png"></p>
 
 ### 3. Make Changes
 
 Change `matplotlib` version from `3.2.2` to `3.3`.
+
 <p align="center"><img width="800" alt="PR_step3" src="https://user-images.githubusercontent.com/26833433/122260853-0a87e980-ced4-11eb-9fd2-3650fb6e0842.png"></p>
 
 ### 4. Preview Changes and Submit PR
@@ -35,6 +38,7 @@ Change `matplotlib` version from `3.2.2` to `3.3`.
 Click on the **Preview changes** tab to verify your updates. At the bottom of the screen select 'Create a **new branch**
 for this commit', assign your branch a descriptive name such as `fix/matplotlib_version` and click the green **Propose
 changes** button. All done, your PR is now submitted to YOLOv5 for review and approval 😃!
+
 <p align="center"><img width="800" alt="PR_step4" src="https://user-images.githubusercontent.com/26833433/122260856-0b208000-ced4-11eb-8e8e-77b6151cbcc3.png"></p>
 
 ### PR recommendations
@@ -70,21 +74,21 @@ understand and use to **reproduce** the problem. This is referred to by communit
 a [minimum reproducible example](https://stackoverflow.com/help/minimal-reproducible-example). Your code that reproduces
 the problem should be:
 
-* ✅ **Minimal** – Use as little code as possible that still produces the same problem
-* ✅ **Complete** – Provide **all** parts someone else needs to reproduce your problem in the question itself
-* ✅ **Reproducible** – Test the code you're about to provide to make sure it reproduces the problem
+- ✅ **Minimal** – Use as little code as possible that still produces the same problem
+- ✅ **Complete** – Provide **all** parts someone else needs to reproduce your problem in the question itself
+- ✅ **Reproducible** – Test the code you're about to provide to make sure it reproduces the problem
 
 In addition to the above requirements, for [Ultralytics](https://ultralytics.com/) to provide assistance your code
 should be:
 
-* ✅ **Current** – Verify that your code is up-to-date with current
+- ✅ **Current** – Verify that your code is up-to-date with current
   GitHub [master](https://github.com/ultralytics/yolov5/tree/master), and if necessary `git pull` or `git clone` a new
   copy to ensure your problem has not already been resolved by previous commits.
-* ✅ **Unmodified** – Your problem must be reproducible without any modifications to the codebase in this
+- ✅ **Unmodified** – Your problem must be reproducible without any modifications to the codebase in this
   repository. [Ultralytics](https://ultralytics.com/) does not provide support for custom code ⚠️.
 
-If you believe your problem meets all of the above criteria, please close this issue and raise a new one using the 🐛 **
-Bug Report** [template](https://github.com/ultralytics/yolov5/issues/new/choose) and providing
+If you believe your problem meets all of the above criteria, please close this issue and raise a new one using the 🐛
+**Bug Report** [template](https://github.com/ultralytics/yolov5/issues/new/choose) and providing
 a [minimum reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) to help us better
 understand and diagnose your problem.