docs: doctest format for example in docstring

Re-writing example in docstring to use [doctest format](https://numpydoc.readthedocs.io/en/latest/format.html#examples).

Minor tpyo in README.md corrected.

README.md

@@ -60,7 +60,7 @@ frames, pixel_to_nanometre_scaling_factor, metadata = load_asd(file_path="./my_a
 
 You can open `.ibw` files using the `load_ibw` function. Just pass in the path to the file
 and the channel name that you want to use. (If in doubt, use `HeightTracee` (yes, with the
-exta 'e'), `ZSensorTrace`, or `ZSensor`).
+extra 'e'), `ZSensorTrace`, or `ZSensor`).
 
 ```python
 from topofileformats.ibw import load_ibw

topofileformats/ibw.py

@@ -63,12 +63,11 @@ def load_ibw(file_path: Path | str, channel: str) -> tuple[np.ndarray, float]:
 
     Examples
     --------
-    ```python
-    from topofileformats.ibw import load_ibw
-    # Load the image and pixel to nanometre scaling factor - HeightTracee is the default channel name
-    # (yes, with the extra e)
-    image, pixel_to_nanometre_scaling_factor = load_ibw(file_path="./my_ibw_file.ibw", channel="HeightTracee")
-    ```
+    Load the image and pixel to nanometre scaling factor - 'HeightTracee' is the default channel name (the extra 'e' is
+    not a typo!).
+
+    >>> from topofileformats.ibw import load_ibw
+    >>> image, pixel_to_nanometre_scaling_factor = load_ibw(file_path="./my_ibw_file.ibw", channel="HeightTracee")
     """
     logger.info(f"Loading image from : {file_path}")
     file_path = Path(file_path)