docs: remove links to pages that are no longer referenced in markdown (#459)

Author: zimeg

README.md

@@ -7,74 +7,25 @@
 Comprehensive documentation is available at [tools.slack.dev/slack-github-action](https://tools.slack.dev/slack-github-action).
 
 Use this GitHub Action to:
-* [Send data with a webhook to start a workflow in Workflow Builder](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-webhook-slack-workflow).
-* [Send data using a Slack API method and a secret token with required scopes](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-slack-api-method/).
-* [Send data as a message with a Slack incoming webhook URL](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-slack-incoming-webhook/).
+
+- [Send data with a webhook to start a workflow in Workflow Builder](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-webhook-slack-workflow).
+- [Send data using a Slack API method and a secret token with required scopes](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-slack-api-method/).
+- [Send data as a message with a Slack incoming webhook URL](https://tools.slack.dev/slack-github-action/sending-techniques/sending-data-slack-incoming-webhook/).
 
 ## Project details
 
 ### Versioning
 
-We recommend using the latest version of this Action for the most recent updates
-and fixes.
+We recommend using the latest version of this Action for the most recent updates and fixes.
 
-Migration guides are available in the [release notes][releases] with breaking
-changes noted between versions.
+Migration guides are available in the [release notes](https://github.com/slackapi/slack-github-action/releases) with breaking changes noted between versions.
 
-Changes required when upgrading from `@v1` to `@v2` are included in this
-[migration guide][v2.0.0].
+Changes required when upgrading from `@v1` to `@v2` are included in this [migration guide](https://github.com/slackapi/slack-github-action/releases/tag/v2.0.0).
 
 ### License
 
 This project is licensed under the [MIT license](LICENSE).
 
 ### Contributing
 
-All contributions are encouraged! Check out the
-[contributor's guide][contributing] to learn more.
-
-[apps]: https://api.slack.com/apps
-[apps-new]: https://api.slack.com/apps/new
-[axios-retry]: https://www.npmjs.com/package/axios-retry
-[block-kit]: https://api.slack.com/surfaces/messages#complex_layouts
-[chat.postMessage]: https://api.slack.com/methods/chat.postMessage
-[chat.update]: https://api.slack.com/methods/chat.update
-[chat:write]: https://api.slack.com/scopes/chat:write
-[config-tokens]: https://api.slack.com/reference/manifests#config-tokens
-[contributing]: .github/contributing.md
-[conversation]: https://api.slack.com/types/conversation
-[custom-api-url]: https://tools.slack.dev/node-slack-sdk/web-api/#custom-api-url
-[epoch]: https://en.wikipedia.org/wiki/Unix_time
-[event-context]: https://github.com/actions/toolkit/blob/main/packages/github/src/context.ts#L6
-[event-payload]: https://docs.github.com/en/webhooks/webhook-events-and-payloads
-[examples]: https://github.com/slackapi/slack-github-action/tree/main/example-workflows
-[files.upload]: https://api.slack.com/messaging/files#upload
-[files.uploadV2]: https://tools.slack.dev/node-slack-sdk/web-api/#upload-a-file
-[flat]: https://www.npmjs.com/package/flat
-[formatting]: https://api.slack.com/reference/surfaces/formatting
-[github-environment]: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables
-[github-outputs]: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/passing-information-between-jobs
-[github-variables]: https://docs.github.com/en/actions/learn-github-actions/variables
-[incoming-webhook]: https://api.slack.com/messaging/webhooks
-[incoming-webhook-scope]: https://api.slack.com/scopes/incoming-webhook
-[interactivity]: https://api.slack.com/messaging/interactivity
-[job-step]: https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#jobsjob_idsteps
-[messaging-parents]: https://api.slack.com/messaging/retrieving#finding_threads
-[messaging-threads]: https://api.slack.com/messaging/sending#threading
-[messaging-timestamp]: https://api.slack.com/messaging/retrieving#individual_messages
-[methods]: https://api.slack.com/methods
-[mrkdwn]: https://api.slack.com/reference/surfaces/formatting
-[plans]: https://slack.com/pricing
-[rate-limits]: https://api.slack.com/apis/rate-limits
-[releases]: https://github.com/slackapi/slack-github-action/releases
-[repo-secret]: https://docs.github.com/en/actions/security-for-github-actions/security-guides/using-secrets-in-github-actions#creating-secrets-for-a-repository
-[response]: https://api.slack.com/web#responses
-[retries]: https://tools.slack.dev/node-slack-sdk/web-api/#automatic-retries
-[retry-after]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After
-[scopes]: https://api.slack.com/scopes
-[slack-web-api]: https://tools.slack.dev/node-slack-sdk/web-api
-[tokens]: https://api.slack.com/concepts/token-types
-[v2.0.0]: https://github.com/slackapi/slack-github-action/releases/tag/v2.0.0
-[variables]: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables
-[wfb]: https://slack.com/features/workflow-automation
-[wfb-create]: https://slack.com/help/articles/360041352714-Build-a-workflow--Create-a-workflow-that-starts-outside-of-Slack
+All contributions are encouraged! Check out the [contributor's guide](.github/contributing.md) to learn more.