Add note that external tools are not managed by Roblox (#1071)

## Changes

This guide makes a reference to several `vscode` extensions, it may be
useful to mention that these tools are not maintained by Roblox, but
instead, the community.

## Checks

By submitting your pull request for review, you agree to the following:

- [x] This contribution was created in whole or in part by me, and I
have the right to submit it under the terms of this repository's open
source licenses.
- [x] I understand and agree that this contribution and a record of it
are public, maintained indefinitely, and may be redistributed under the
terms of this repository's open source licenses.
- [x] To the best of my knowledge, all proposed changes are accurate.

---------

Author: metatablecat

content/en-us/projects/external-tools.md

@@ -7,6 +7,8 @@ For professional development studios, setting up third-party tools and investing
 
 <Alert severity="info">
 Although this page covers several popular tools, it shouldn't be taken as a strict recommendation of them. Every team has different needs, so this page is intended to help you examine ways to improve your workflow rather than tell you to download anything in particular.
+
+Tools mentioned on this page are not maintained by Roblox and may change or stop working at any time.
 </Alert>
 
 ## The syncing problem