fix (minor): update contribution guide wiki links

[jtbg]

Amplitude Developer Docs PR

Description

• DDI-369: Update Readme and remove extra files #508 migrated the meta-docs to the github repository's wiki.
• This change updates the contribution guide with corrected links to the style guide and format cheatsheet

Note that links to the wiki pages must be full URLs; relative links are not supported.

Deadline

non-urgent

Change type

• Doc bug fix.
• Doc update.
• New documentation.
• Non-documentation related fix or update.

PR checklist:

• My documentation follows the style guidelines of this project.
• I previewed my documentation on a local server using mkdocs serve.
• Running mkdocs serve didn't generate any failures.
• I have performed a self-review of my own documentation.

@amplitude-dev-docs

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