Fix broken link in README referencing date and time configuration

Fix broken link referencing zsh date and time configuration in prompt expansion. 

The current broken link points to `http://zsh.sourceforge.net/Doc/Release Prompt-Expansion.html`, while the correct link is http://zsh.sourceforge.net/Doc/Release/Prompt-Expansion.html#Date-and-time

README.md

@@ -374,7 +374,7 @@ The `date` segment shows the current system date.
 
 | Variable | Default Value | Description |
 |----------|---------------|-------------|
-|`POWERLEVEL9K_DATE_FORMAT`|`%D{%d.%m.%y}`|[ZSH time format](http://zsh.sourceforge.net/Doc/Release Prompt-Expansion.html) to use in this segment.|
+|`POWERLEVEL9K_DATE_FORMAT`|`%D{%d.%m.%y}`|[ZSH time format](http://zsh.sourceforge.net/Doc/Release/Prompt-Expansion.html#Date-and-time) to use in this segment.|
 
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