chore(doc): auto generate docs

doc/CopilotChat.txt

@@ -293,6 +293,49 @@ You can define custom contexts like this:
 <
 
 
+SELECTIONS ~
+
+Selections are used to determine the source of the chat (so basically what to
+chat about). Selections are configurable either by default or by prompt.
+Default selection is `visual` or `buffer` (if no visual selection). Default
+supported selections that live in `local select =
+require("CopilotChat.select")` are:
+
+- `select.visual` - Current visual selection. Works well with diffs.
+- `select.buffer` - Current buffer content. Works well with diffs.
+- `select.line` - Current line content. Works decently with diffs.
+- `select.unnamed` - Content from the unnamed register.
+- `select.clipboard` - Content from system clipboard.
+
+You can define custom selection functions like this:
+
+>lua
+    {
+      selection = function()
+        -- Get content from * register
+        local lines = vim.fn.getreg('*')
+        if not lines or lines == '' then
+          return nil
+        end
+
+        return {
+          lines = lines,
+        }
+      end
+    }
+<
+
+Or chain multiple selections like this:
+
+>lua
+    {
+      selection = function(source)
+        return select.visual(source) or select.buffer(source)
+      end
+    }
+<
+
+
 API ~
 
 >lua