docs(readme): add description

README.md

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 <p align="center"><img alt="exponential-buckets-explorer" src="https://github.com/DDtKey/exponential-buckets-explorer/raw/main/assets/images/logo.png"></p>
+
+A simple web page and desktop application for calculating buckets based on the exponential function.
+
+Available at [buckets-exp.ddtkey.com](https://buckets-exp.ddtkey.com/), the desktop version can be downloaded from the release page: [latest](https://github.com/DDtKey/exponential-buckets-explorer/releases/latest)
+
+Can be useful for checking parameters when configuring histograms in Prometheus, for example:
+- rust: [exponential_buckets](https://docs.rs/prometheus/0.13.3/prometheus/fn.exponential_buckets.html)
+- go: [ExponentialBuckets](https://pkg.go.dev/github.com/prometheus/client_golang/prometheus#ExponentialBuckets)
+
+The application is built on [Leptos] and [Tauri].
+
+
+[Leptos]: https://github.com/leptos-rs/leptos
+[Tauri]: https://github.com/tauri-apps/tauri