docs: add details about is binary functions

README.md

@@ -19,4 +19,29 @@ go get github.com/shelepuginivan/fsutil
 
 ## Documentation
 
-Is available on [pkg.go.dev](https://pkg.go.dev/github.com/shelepuginivan/fsutil)
+Is available on [pkg.go.dev](https://pkg.go.dev/github.com/shelepuginivan/fsutil).
+
+## Details about `IsBinary`, `IsBinarySlow` and `IsBinaryFast`
+
+> [!NOTE]
+> Available since `v0.2.0`.
+
+Each `IsBinary`, `IsBinarySlow` and `IsBinaryFast` report whether data is
+binary, i.e. a non human-readable text, such as image, audio or video stream.
+
+- `IsBinarySlow` has the **best accuracy** and the **worst speed**, since it
+  checks the entire byte sequence.
+- `IsBinaryFast` has the **worst accuracy** and the **best speed** since it
+  checks only first line of the sequence.
+- `IsBinary` is in the middle — it checks the first and every 2^N line
+  (i.e. 0, 1, 2, 4, 8, 16, etc.), providing a good accuracy while keeping good
+  performance.
+
+The table below shows the accuracy of these functions, determined by testing
+against random byte sequences:
+
+|    Function    |   Mimimal accuracy   |   Actual accuracy    |
+| :------------: | :------------------: | :------------------: |
+| `IsBinary`     |  990/1000 (`99.0%`)  | 1000/1000 (`100.0%`) |
+| `IsBinarySlow` | 1000/1000 (`100.0%`) | 1000/1000 (`100.0%`) |
+| `IsBinaryFast` |  950/1000 (`95.0%`)  |  991/1000 (`99.1%`)  |