Overhaul documentation

[PatrickF1]

• Refer to "search features" as "search commands", which is clearer.
• Clearly give each search command a capitalized, canonical name so it can be clearly referred to in the rest of the docs.
• Explicitly call out the "type" of the output of each command to be unambiguous.
• Add emojis in search command docs so they are more distinguishable when quickly scrolling.
• Make configuration docs more concise and clearer.
• Point out fd and bat only need to be installed if using Search Directory.