Hi!

In elixir, the docs in src are like this:

``` elixir-ts-mode
defmodule Foo do
  @moduledoc """
  Foo-related functions.

  ## Examples

      iex> Foo.sum(1, 2)
      3
  """

  @doc """
  Calculate the sum of two numbers.
  """
  def sum(a, b), do: a + b
end
```

In python-mode, input the continious triple quotes, it will insert the
left quotes when electric-pair-mode is on.

python-mode did it here:

https://github.com/emacs-mirror/emacs/blob/bfa3500c3c6e4df58978e84753718cd5358c06fb/lisp/progmodes/python.el#L6599-L6607

https://github.com/emacs-mirror/emacs/blob/bfa3500c3c6e4df58978e84753718cd5358c06fb/lisp/progmodes/python.el#L6637-L6639

This behavior is also very common in elixir, so can we add this to
elixir-ts-mode? thx