[Backport] Backporting documentation URL fix for 1381488

[brett-groshong]

Please read the Contributing guide before making a PR.

• Read the Graphics repository & Yamato FAQ.

---

Purpose of this PR

Why is this PR needed, what hard problem is it solving/fixing?
Backport of documentation URL update for 1381488.
Original PR #6665

Testing status

Describe what manual/automated tests were performed for this PR
Opened in 2021.2.7f1 (current external) and verified that doc link works.

---

Comments to reviewers

Notes for the reviewers you have assigned.

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://unity-ci.cds.internal.unity3d.com/project/902/
Search for your PR branch using the search bar at the top, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

Shader Graph
/jobDefinition/.yamato%252Fall-shadergraph.yml%2523PR_ShaderGraph_2021.2
Depending on your PR, you may also want
/jobDefinition/.yamato%252Fall-shadergraph_builtin_foundation.yml%2523PR_ShaderGraph_BuiltIn_Foundation_2021.2
/jobDefinition/.yamato%2Fall-shadergraph_builtin_lighting.yml%23PR_ShaderGraph_BuiltIn_Lighting_2021.2

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.