Add Emacs screenshot, add Emacs to IDE doc page

docs/ide.rst

@@ -21,6 +21,7 @@ IDE Integration
     ide/atom
     ide/clion
     ide/eclipse
+    ide/emacs
     ide/energia
     ide/qtcreator
     ide/sublimetext

docs/ide/emacs.rst

@@ -69,3 +69,9 @@ There are 4 predefined targets for building.
     The libraries which are added, installed or used in the project
     after generating process wont be reflected in IDE. To fix it you
     need to reinitialize project using :ref:`cmd_init` (repeat it).
+
+
+Screenshot
+----------
+
+.. image:: ../_static/ide-platformio-emacs.png