docs: Add API routes

Signed-off-by: Julien Riou <julien@riou.xyz>

src/cmd/collerd/README.md

@@ -32,4 +32,44 @@ The file format is **JSON**:
 * **prometheus_notes_metric** (string): Name of the notes count metric (default "collerd_notes")
 * **observation_internal** (int): Number of seconds to wait between two observations (default 60)
 
-The configuration file is not required but the service might not be exposed to the public.
+The configuration file is not required but the service might not be exposed to the public.
+
+## API
+
+### GET /health
+
+Returns 200 OK.
+
+### POST /api/note
+
+Create a note.
+
+Body (JSON):
+* **content** (string): base64 encoded content (required)
+* **password** (string): user-provided password
+* **encrypted** (bool): true if the note has been encrypted by the client
+* **expiration** (int): lifetime of the note in seconds (must be supported by the server)
+* **delete_after_read** (bool): delete the note after the first read
+
+Response (JSON):
+* **id** (string): ID of the note
+
+
+### GET /<id>/<password>
+
+> [!IMPORTANT]
+> Potential password leak
+
+Return content of a note encrypted by the given password.
+
+### GET /<id>
+
+Return content of a note.
+
+If the note is encrypted, the encrypted value is returned (application/octet-stream). Otherwise, the text is returned (text/plain).
+
+### Errors
+
+Errors return **500 Server Internal Error** with the **JSON** payload:
+* **message** (string): message of the response
+* **error** (string): error if any