Update Social login docs for custom mobile SDKs

[nkshah2]

Summary of change

(A few sentences about this PR)

Related issues

• Link to issue1 here
• Link to issue1 here

Checklist

• [ ] Algolia search needs to be updated? (If there is a new sub docs project, then yes)
• [ ] Sitemap needs to be updated? (If there is a new sub docs project, then yes)
• [ ] Checked for broken links? (Run cd v2 && MODE=production npx docusaurus build)
• [ ] Changes required to the demo apps corresponding to the docs?

Remaining TODOs for this PR

• [ ] Item1
• [ ] Item2

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