Update nav2_bringup docs to include updated robot string.

[leander-dsouza]

---

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#5000
Primary OS tested on	Ubuntu
Robotic platform tested on	N/A
Does this PR contain AI generated software?	No

---

Description of contribution in a few bullet points

• Updated the nav2_bringup docs to include the updated robot string.

Description of documentation updates required from your changes

• The documented change is currently in a PR at the docs repository.

Description of how this change was tested

• The command mentioned in the README was pasted on the terminal to check if any formatting issues was present and verified.

---

Future work that may be required in bullet points

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists

[SteveMacenski]

Why a draft?

[SteveMacenski]

#5000

Also congrats, that's the 5000's PR/issue in Nav2 🥳

[leander-dsouza]

Why a draft?

Ah, just a force of habit to be wary of any failing CI pipelines :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

see 9 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.