remove Atom and change to bulleted list

Test plan:
run `make html` and inspect generated documentation.

doc/user-manual/tools/emacs-mode.rst

@@ -6,12 +6,16 @@ Emacs Mode
 
 Agda programs are commonly edited using `Emacs
 <http://www.gnu.org/software/emacs/>`_ which is explained in this
-section.  Other editors with interactive support for Agda include Atom
-(`agda-mode on Atom <https://atom.io/packages/agda-mode>`_), Visual
-Studio Code (`agda-mode on VS Code
-<https://github.com/banacorn/agda-mode-vscode>`_), Neovim (`Cornelis
-<https://github.com/isovector/cornelis>`_), and Vim (`agda-vim
-<https://github.com/derekelkins/agda-vim>`_).
+section.  Other editors with interactive support for Agda include
+
+* Visual Studio Code (`agda-mode on VS Code
+  <https://github.com/banacorn/agda-mode-vscode>`_)
+
+* Neovim (`Cornelis
+  <https://github.com/isovector/cornelis>`_), and
+
+* Vim (`agda-vim
+  <https://github.com/derekelkins/agda-vim>`_)
 
 To edit a module in Emacs (assuming you have :ref:`installed
 <installation>` Agda and the Emacs mode properly), open a file ending