Update and rename messaging-basics.md to messaging-basics.rst

Author: lfbrock

source/help/getting-started/messaging-basics.md

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+Messaging Basics
+================
+
+--------------
+
+**Write messages** using the text input box at the bottom of Mattermost.
+Press **ENTER** to send a message. Use **Shift+ENTER** to create a new
+line without sending a message.
+
+**Reply to messages** by clicking the reply arrow next to the message
+text.
+
+.. image:: ../../images/replyIcon.PNG
+   :alt: reply arrow
+
+**Notify teammates** when they are needed by typing ``@username``.
+
+**Format your messages** using Markdown that supports text styling,
+headings, links, emoticons, code blocks, block quotes, tables, lists and
+in-line images.
+
+.. image:: ../../images/messagesTable1.PNG
+   :alt: markdown
+
+**Quickly add emoji** by typing ":", which will open an emoji
+autocomplete. If the existing emoji don't cover what you want to
+express, you can also create your own `Custom
+Emoji <http://docs.mattermost.com/help/settings/custom-emoji.html>`__.
+
+**Attach files** by dragging and dropping into Mattermost or clicking
+the attachment icon in the text input box.
+
+**Flag messages for follow up** by clicking the flag icon next to the
+message timestamp.
+
+.. figure:: ../../images/flagicon.png
+   :alt: flags
+
+Learn more about: 
+
+* `Composing Messages and Replies <http://docs.mattermost.com/help/messaging/sending-messages.html>`__
+* `Mentioning Teammates <http://docs.mattermost.com/help/messaging/mentioning-teammates.html>`__
+* `Formatting Messages using Markdown <http://docs.mattermost.com/help/messaging/formatting-text.html>`__
+* `Attaching Files <http://docs.mattermost.com/help/messaging/attaching-files.html>`__
+* `Executing Commands <http://docs.mattermost.com/help/messaging/executing-commands.html>`__