todo.sr.ht: Document sorting

todo.sr.ht/index.md

@@ -32,14 +32,37 @@ include:
 - `status:open` or `status:closed`
 - `label`: an optional label that is assigned to a ticket for organizational
   purposes
-- `order`: the order in which tickets are displayed. By default this is by
-  time of last update
 - `submitter`: the user who submitted the ticket. Use `me` to find tickets
   submitted by yourself
 - `assigned`: tickets that are assigned to a particular user
 - `no:assignee`: tickets not assigned to anyone
 - `no:label`: tickets with no labels
 
+Use the negation prefix `!` to inverse any filter. For example:
+
+- `!assigned:me`: tickets which are not assigned to me
+- `!no:label`: tickets which have at least one label applied
+
+## Sorting tickets
+
+By default, tickets are sorted by most recently updated. To change the sort
+order, enter one of:
+
+- `sort:created` - sort by creation time
+- `sort:updated` - sort by last updated time
+- `sort:comments` - sort by the number of comments
+
+Sort direction is descending by default and can be reversed by using `rsort`
+instead of `sort`:
+
+- `sort:updated` - sort descending
+- `rsort:updated` - sort ascending
+
+It's possible to specify multiple sorting criteria:
+
+- `sort:comments sort:created` - sort first by number of comments, then by
+  creation time
+
 # Tickets
 
 Each ticket has its own page and number. On the ticket page, you can comment