Add link to new file upload methods

[technically-tracy]

Summary

Add links to files.upload v2 details.

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs-src (Documents, have you run ./scripts/docs.sh?)
• /docs-src-v2 (Documents, have you run ./scripts/docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.34%. Comparing base (f8906fe) to head (008663c).

❗ Current head 008663c differs from pull request most recent head d78e9d9. Consider uploading reports for the commit d78e9d9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1489      +/-   ##
==========================================
- Coverage   85.35%   85.34%   -0.01%     
==========================================
  Files         111      111              
  Lines       12291    12291              
==========================================
- Hits        10491    10490       -1     
- Misses       1800     1801       +1     

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Updated link

[filmaj]

Looks good but the source for the docs actually exist under the docs-src/ directory.

More information on this particular setup in the maintainer's guide for this repository.

So I think what you want to do is:

1. Make your suggested change in the docs-src directory.
2. Run the doc generation as described in the maintainer's guide.
3. Commit your changes to docs-src as well as the doc-generation changes to the docs directory in this PR.

I think that's how it's supposed to work? @WilliamBergamin / @seratch can you confirm? I am a bit confused about this as well, so maybe it would be good to slightly expand on the doc-generation section of the maintainer's guide to elaborate. For example, it was unclear to me whether the doc generation happens automatically as part of CI/CD or not.

[WilliamBergamin]

Thank you for the contribution 💯
Yess I believe the changes need to be done in docs-src/, the docs generation script (./scripts/docs.sh) will generate the contents of doc/ from the source code in docs-src/

You can test out your changes in docs-src/ locally by running ./scripts/generate_api_docs.sh

[technically-tracy]

Thank you both for all the great information! I'll close this PR and try out the steps in the maintainer's guide.