Docs: always use <> tags for placeholders in man pages

doc/man/task.1.in

@@ -151,12 +151,12 @@ the specified month and year.  If the 'due' argument is provided, will show
 the starting month of the earliest due task.
 
 .TP
-.B task colors [sample | legend]
+.B task colors [<sample> | legend]
 Displays all possible colors, a named sample, or a legend containing all
 currently defined colors.
 
 .TP
-.B task columns [substring]
+.B task columns [<substring>]
 Displays all supported columns and formatting styles.  Useful when creating
 custom reports.  If a substring is provided, only matching column names are
 shown.
@@ -431,7 +431,7 @@ Examples:
     2015-03-31T23:59:59
 
 .TP
-.B task config [name [value | '']]
+.B task config [<name> [<value> | '']]
 Add, modify and remove settings directly in the Taskwarrior configuration.
 This command either modifies the 'name' setting with a new value of 'value',
 or adds a new entry that is equivalent to 'name=value':
@@ -516,7 +516,7 @@ Lists all supported reports.  This includes the built-in reports, and any custom
 reports you have defined.
 
 .TP
-.B task show [all | substring]
+.B task show [all | <substring>]
 Shows all the current settings.  If a
 substring is specified just the settings containing that substring will be
 displayed.
@@ -556,7 +556,7 @@ notation for other task metadata. It is an error to attempt to add or remove a
 virtual tag.
 
 .TP
-.B task timesheet [weeks]
+.B task timesheet [<weeks>]
 Shows a weekly report of tasks completed and started.
 
 .TP