Document filter and modification syntax

cli/src/argparse/filter.rs

@@ -1,6 +1,8 @@
 use super::args::{arg_matching, id_list, minus_tag, plus_tag, TaskId};
 use super::ArgList;
+use crate::usage;
 use nom::{branch::alt, combinator::*, multi::fold_many0, IResult};
+use textwrap::dedent;
 
 /// A filter represents a selection of a particular set of tasks.
 ///
@@ -110,6 +112,36 @@ impl Filter {
         }
         map_res(arg_matching(minus_tag), to_filterarg)(input)
     }
+
+    pub(super) fn get_usage(u: &mut usage::Usage) {
+        u.filters.push(usage::Filter {
+            syntax: "TASKID[,TASKID,..]".to_owned(),
+            summary: "Specific tasks".to_owned(),
+            description: dedent(
+                "
+                Select only specific tasks.  Multiple tasks can be specified either separated by
+                commas or as separate arguments.  Each task may be specfied by its working-set
+                index (a small number) or by its UUID.  Prefixes of UUIDs broken at hyphens are
+                also supported, such as `b5664ef8-423d` or `b5664ef8`.",
+            ),
+        });
+        u.filters.push(usage::Filter {
+            syntax: "+TAG".to_owned(),
+            summary: "Tagged tasks".to_owned(),
+            description: dedent(
+                "
+                Select tasks with the given tag.",
+            ),
+        });
+        u.filters.push(usage::Filter {
+            syntax: "-TAG".to_owned(),
+            summary: "Un-tagged tasks".to_owned(),
+            description: dedent(
+                "
+                Select tasks that do not have the given tag.",
+            ),
+        });
+    }
 }
 
 #[cfg(test)]

cli/src/argparse/mod.rs

@@ -31,4 +31,6 @@ type ArgList<'a> = &'a [&'a str];
 
 pub(crate) fn get_usage(usage: &mut Usage) {
     Subcommand::get_usage(usage);
+    Filter::get_usage(usage);
+    Modification::get_usage(usage);
 }

cli/src/argparse/modification.rs

@@ -1,8 +1,10 @@
 use super::args::{any, arg_matching, minus_tag, plus_tag};
 use super::ArgList;
+use crate::usage;
 use nom::{branch::alt, combinator::*, multi::fold_many0, IResult};
 use std::collections::HashSet;
 use taskchampion::Status;
+use textwrap::dedent;
 
 #[derive(Debug, PartialEq, Clone)]
 pub enum DescriptionMod {
@@ -107,6 +109,34 @@ impl Modification {
         }
         map_res(arg_matching(minus_tag), to_modarg)(input)
     }
+
+    pub(super) fn get_usage(u: &mut usage::Usage) {
+        u.modifications.push(usage::Modification {
+            syntax: "DESCRIPTION".to_owned(),
+            summary: "Set description".to_owned(),
+            description: dedent(
+                "
+                Set the task description.  Multiple arguments are combined into a single
+                space-separated description.",
+            ),
+        });
+        u.modifications.push(usage::Modification {
+            syntax: "+TAG".to_owned(),
+            summary: "Tag task".to_owned(),
+            description: dedent(
+                "
+                Add the given tag to the task.",
+            ),
+        });
+        u.modifications.push(usage::Modification {
+            syntax: "-TAG".to_owned(),
+            summary: "Un-tag task".to_owned(),
+            description: dedent(
+                "
+                Remove the given tag from the task.",
+            ),
+        });
+    }
 }
 
 #[cfg(test)]

cli/src/argparse/subcommand.rs

@@ -243,7 +243,7 @@ impl Modify {
         });
         u.subcommands.push(usage::Subcommand {
             name: "stop".to_owned(),
-            syntax: "[filter] start [modification]".to_owned(),
+            syntax: "[filter] stop [modification]".to_owned(),
             summary: "Stop tasks".to_owned(),
             description: dedent(
                 "
@@ -252,7 +252,7 @@ impl Modify {
         });
         u.subcommands.push(usage::Subcommand {
             name: "done".to_owned(),
-            syntax: "[filter] start [modification]".to_owned(),
+            syntax: "[filter] done [modification]".to_owned(),
             summary: "Mark tasks as completed".to_owned(),
             description: dedent(
                 "