Doc fix for fable template

[austingmhuang]

Context:
As pointed out by @isaacdevlugt, Fable template docs are unclear regarding the number of wires needed. This seeks to clarify that.

Description of the Change:
Docs changed to reflect that the # of wires needed is 2n+1

Benefits:
Users don't get confused by the seemingly random additional wire

Possible Drawbacks:

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[isaacdevlugt]

🙌 thanks guys!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.68%. Comparing base (9151477) to head (0050853).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5577      +/-   ##
==========================================
- Coverage   99.69%   99.68%   -0.01%     
==========================================
  Files         410      411       +1     
  Lines       38278    38015     -263     
==========================================
- Hits        38161    37897     -264     
- Misses        117      118       +1     

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