Ability to view markdown without clicking on them in file explorer.

[dwivedi-ritik]

Hi there

This is the change for this feature Add an auto-view mode .
Though its half the feature whats propose.

Thanks :)

Feature Change:

• Ability to view markdown without clicking on them directory tree.
• Ability to focus the viewer with enter key.

Modified

• screens/main.py
• widgets/viewer.py
• widgets/navigation_panes/local_files.py