tsk-35: Add API documentation (#39)

Closes #35

Reviewed-on: phoenix/textsender-api#39
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

Dockerfile

@@ -29,6 +29,7 @@ COPY ./internal ./internal
 COPY ./Makefile .
 COPY ./.env .
 COPY ./migrations ./migrations
+COPY ./docs ./docs
 
 # Build the application
 RUN CGO_ENABLED=0 GOOS=linux make build