display downloadable files

When making the notebook where I included the Downloader class, I noticed it was not possible to easily display the downloadable files. In this branch I have mad a class function that prints the info in a nice format - it collects it from the page, so it updates, when more data is added.

qim3d/io/_downloader.py

@@ -17,6 +17,9 @@ class Downloader:
 
     Attributes:
         folder_name (str or os.PathLike): Folder class with the name of the folder in <https://data.qim.dk/>
+    
+    Methods:
+        file_directory(): Prints the downloadable files from the QIM data repository.
 
     Syntax for downloading and loading a file is `qim3d.io.Downloader().{folder_name}.{file_name}(load_file=True)`
 
@@ -50,6 +53,7 @@ class Downloader:
         import qim3d
         
         downloader = qim3d.io.Downloader()
+        downloader.file_directory()        
         data = downloader.Cowry_Shell.Cowry_DOWNSAMPLED(load_file=True)
 
         qim3d.viz.slicer_orthogonal(data, color_map="magma")