Update web terminal note for shared runners

What does this MR do?

Update web terminal note for shared runners.

The current documentation suggests that a user can not use his own runner for a specific group or project. At first, I thought this was the case but it is not true since we do allow websocket connections on GitLab.com, this was discovered as part of the investigation on #52611 (moved).

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Tested in all supported browsers
• [-] Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• [-] Security reports checked/validated by reviewer