z: add -c parameter to the command description (#5262)

pages/common/z.md

@@ -1,6 +1,6 @@
 # z
 
-> Tracks the most used directories and enables quickly navigating to them using string or regex patterns.
+> Tracks the most used (by frecency) directories and enables quickly navigating to them using string or regex patterns.
 > More information: <https://github.com/rupa/z>.
 
 - Go to a directory that contains "foo" in the name:
@@ -26,3 +26,7 @@
 - Remove the current directory from `z`'s database:
 
 `z -x .`
+
+- Restrict matches to subdirectories of the current directory:
+
+`z -c {{foo}}`