doc: improve documentation for set_sort (#401)

doc/api.md

@@ -59,9 +59,14 @@ Change the display columns for oil
 `set_sort(sort)` \
 Change the sort order for oil
 
-| Param | Type       | Desc |
-| ----- | ---------- | ---- |
-| sort  | `string[]` | []   |
+| Param | Type             | Desc                                                                                  |
+| ----- | ---------------- | ------------------------------------------------------------------------------------- |
+| sort  | `oil.SortSpec[]` | List of columns plus direction. See :help oil-columns to see which ones are sortable. |
+
+**Examples:**
+```lua
+require("oil").set_sort({ { "type", "asc" }, { "size", "desc" } })
+```
 
 ## set_is_hidden_file(is_hidden_file)
 

doc/oil.txt

@@ -255,7 +255,12 @@ set_sort({sort})                                                    *oil.set_sor
     Change the sort order for oil
 
     Parameters:
-      {sort} `string[]` []
+      {sort} `oil.SortSpec[]` List of columns plus direction. See :help oil-
+             columns to see which ones are sortable.
+
+    Examples: >lua
+      require("oil").set_sort({ { "type", "asc" }, { "size", "desc" } })
+<
 
 set_is_hidden_file({is_hidden_file})                      *oil.set_is_hidden_file*
     Change how oil determines if the file is hidden

lua/oil/init.lua

@@ -121,7 +121,9 @@ M.set_columns = function(cols)
 end
 
 ---Change the sort order for oil
----@param sort string[][]
+---@param sort oil.SortSpec[] List of columns plus direction. See :help oil-columns to see which ones are sortable.
+---@example
+--- require("oil").set_sort({ { "type", "asc" }, { "size", "desc" } })
 M.set_sort = function(sort)
   require("oil.view").set_sort(sort)
 end