Sentence case for Markdown in Keyboard Shortcut Table

For consistency with other strings:

1. Should Show Formatting be changed to Show formatting (lowercase f)
2. Should Show Preview be changed to Show preview (lowercase p)

Thank you

Linux Mint 21.2 Cinnamon
Jami Version: 202307311645

https://review.jami.net/c/jami-client-qt/+/25443

added sprintto review label

assigned to @agsantos

mentioned in commit 7f2c98a5

added sprintdone label and removed sprintto review label

closed

removed sprintdone label