Better README & getting started (#2284)

* initial

* wip

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* pr comment

* remove todo

* add a few placeholders

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docs/dev/api.md

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+# API
+
+API for external projects to access sendou.ink data for projects such as streams is available. This API is for reading data, writing is not supported. You will need a token to access the API. Currently access is limited but you can request a token from Sendou.
+
+## Endpoints
+
+Check out `sendou.ink/app/features/api-public/schema.ts`
+
+## Curl example
+
+```bash
+sendou@macbook ~ % curl -H "Authorization: Bearer mytoken" https://sendou.ink/api/tournament/1 
+{"name":"PICNIC mini","startTime":"2023-05-18T18:00:00.000Z","url":"https://sendou.ink/to/1/brackets","logoUrl":"https://sendou.ink/static-assets/img/tournament-logos/pn.png","teams":{"checkedInCount":25,"registeredCount":31},"brackets":[{"name":"Main bracket","type":"double_elimination"}],"organizationId":1,"isFinalized":true}% 
+```
+
+## Clients (unofficial)
+
+- [sendou.py (Python)](https://github.com/IPLSplatoon/sendou.py)