chore: Add Starknet Core Contract to starknet_docs_style_guide.adoc

[stoobie]

Description of the Changes

Add Starknet Core Contract to starknet_docs_style_guide.adoc

PR Preview URL

https://github.com/starknet-io/starknet-docs/blob/steve/style_guide/Starknet_Core_Contract/contributing_to_docs/starknet_docs_style_guide.adoc

Check List

• [x] Changes have been done against main branch, and PR does not conflict
• [x] PR title follows the convention: <docs/feat/fix/chore>(optional scope): <description>, e.g: fix: minor typos in code

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This change is 

[github-actions[bot]]

Your preview build is ready! ✨ Check the following link in 1-2 minutes: https://starknet-io.github.io/starknet-docs/pr-1215/documentation/ .

[github-actions[bot]]

Your preview build is ready! ✨ Check the following link in 1-2 minutes: https://starknet-io.github.io/starknet-docs/pr-1215/documentation/ .