Updates man page documentation

[LangLangBart]

docs(man): Add example for {+f} in preview command

Provide an example for having multiple selected items be seperated by newlines,
as the question comes up from time to time.

References:

• fzf run command as result #4604
• Copy selected items to clipboard #4187

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docs(man): replace echo -e with printf to improve portability across different shells

echo -e behaves inconsistently across different shells.

References:

• Feedback romkatv/zsh4humans#35 (comment)
• https://www.in-ulm.de/~mascheck/various/echo+printf/

For example:
/bin/sh -c 'echo -e 1' -> -e 1
/bin/dash -c 'echo -e 2' -> -e 2
/bin/bash -c 'echo -e 3' -> 3

While POSIX 2024 added text regarding -e support, it does not guarantee
consistent behavior across different shells. printf is the recommended
portable alternative for formatted output and escape sequences.

References:

• https://www.austingroupbugs.net/view.php?id=1222
• https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/utilities/echo.html#tag_20_37_18
• https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/utilities/echo.html#tag_20_37_18

[junegunn]

Merged, thanks!