docs: fix typo in glossary link (#397)

# Purpose
There's a small typo in the [**What is
Unraid**](https://docs.unraid.net/unraid-os/getting-started/what-is-unraid/#)
section.
<img width="359" height="30" alt="image"
src="https://github.com/user-attachments/assets/db4b2195-577a-4994-a2e7-0871822d1c67"
/>


To find it, please go to: 

- Software-defined NAS **&rarr;** Arrays and Parity **&rarr;** How
Parity Works

In the repository, this typo occurs under the parity section in the
`what-is-unraid.mdx` file. You can just ctrl f for "we need a fourth
disk as"

## Fix
Add an `s` to `%%parity disk|parity-drive%%` **&rarr;** `%%parity
disk|parity-drives%%`

## Current Prod:
<img width="819" height="213" alt="image"
src="https://github.com/user-attachments/assets/dcb89848-c3d4-41fc-8cbf-0a243961b508"
/>


## After Typo Fix:
<img width="817" height="283" alt="image"
src="https://github.com/user-attachments/assets/da5ccd9a-6735-4975-b58d-a0050116f9f3"
/>



Before Submitting This PR, Please Ensure You Have Completed The
Following:

1. [x] Are internal links to wiki documents using [relative file
links](https://docusaurus.io/docs/markdown-features/links)?
2. [x] Are all new documentation files lowercase, with dash separated
names (ex. unraid-os.mdx)?
3. [x] Are all assets (images, etc), located in an assets/ subfolder
next to the .md/mdx files?
4. [x] Have you checked to ensure there aren't other open [Pull
Requests](../../../pulls) for the same update/change?
5. [x] Is the build succeeding?


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Corrected terminology references in documentation for improved
consistency.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: Ajit-Mehrotra

docs/unraid-os/getting-started/what-is-unraid.mdx

@@ -33,7 +33,7 @@ Unraid features a [user-friendly web interface](./explore-the-user-interface/tou
       ![No Parity](/img/No_parity_500px.png)
     </div>
 
-    In the image above, three drives contain streams of bits that vary by device size.  These drives are unprotected, so if one fails, data will be lost.  To protect against failure, we need a fourth disk as a %%parity disk|parity-drive%%, which must be equal to or larger than the largest data disk.
+    In the image above, three drives contain streams of bits that vary by device size.  These drives are unprotected, so if one fails, data will be lost.  To protect against failure, we need a fourth disk as a %%parity disk|parity-drives%%, which must be equal to or larger than the largest data disk.
 
     To set the %%parity|parity%% bits, we find the total for each column.  If the sum is even, the %%parity|parity%% bit is 0; if odd, the %%parity|parity%% bit is 1.