nvim: Update checkbox markdown states

We now have the usual 'undone' ([ ]) and 'done' ([x]) states, but
express 3 further ones that are _somewhat_ standardized:

- [o] this one is 'doing', in-progress
- [-] this one is 'indeterminate', we're not sure
- [~] this one is 'deleted', never to be done

nvim/.config/nvim/lua/plugins/prose.lua

@@ -80,8 +80,9 @@ local prose_plugs = {
 			},
 			checkbox = {
 				custom = {
-					todo = { raw = "[-]", rendered = "󰡖 ", highlight = "RenderMarkdownTodo" },
-					removed = { raw = "[_]", rendered = "󱋭 ", highlight = "RenderMarkdownTodo" },
+					doing = { raw = "[o]", rendered = "󰡖 ", highlight = "RenderMarkdownTodo" },
+					indeterminate = { raw = "[-]", rendered = "󰄗 ", highlight = "RenderMarkdownTodo" },
+					removed = { raw = "[~]", rendered = "󱋭 ", highlight = "RenderMarkdownTodo" },
 				},
 			},
 			html = {