chore(edit-docs): move Markdown documentation outside src for now

docs/User Guide/User Guide/Advanced Usage/ETAPI (REST API).md

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+# ETAPI (REST API)
+ETAPI is Trilium's public/external REST API. It is available since Trilium v0.50.
+
+The documentation is in OpenAPI format, available [here](https://github.com/TriliumNext/Notes/blob/master/src/etapi/etapi.openapi.yaml).
+
+[trilium-py](https://github.com/Nriver/trilium-py) is a third-party Python implementation for ETAPI client, you can use Python to communicate with Trilium.
+
+## Authentication
+
+All operations have to be authenticated using a token. You can get this token either from Options -> ETAPI or programmatically using the `/auth/login` REST call (see the [spec](https://github.com/TriliumNext/Notes/blob/master/src/etapi/etapi.openapi.yaml)):
+
+```
+GET https://myserver.com/etapi/app-info
+Authorization: ETAPITOKEN
+```
+
+Alternatively, since 0.56 you can also use basic auth format:
+
+```
+GET https://myserver.com/etapi/app-info
+Authorization: Basic BATOKEN
+```
+
+*   Where `BATOKEN = BASE64(username + ':' + password)` - this is a standard Basic Auth serialization
+*   Where `username` is "etapi"
+*   And `password` is the generated ETAPI token described above.
+
+Basic Auth is meant to be used with tools which support only basic auth.