Add installation instructions

Now that splunk-mode has been released on MELPA, should add details on
how to install.

README.md

@@ -1,3 +1,28 @@
 <h1 align="center">splunk-mode</h1>
 
-Syntax highlighting for Splunk in Emacs
+[![MELPA Status](https://melpa.org/packages/splunk-mode-badge.svg)](https://melpa.org/#/splunk-mode)
+[![MELPA Stable Status](https://stable.melpa.org/packages/splunk-mode-badge.svg)](https://stable.melpa.org/#/splunk-mode)
+[![Build Status](https://github.com/jakewilliami/splunk-mode/actions/workflows/test.yml/badge.svg)](https://github.com/jakewilliami/splunk-mode/actions/workflows/test.yml)
+
+[Emacs](https://www.gnu.org/software/emacs/) major mode for editing [Splunk SPL](https://splunk.com/) source code.
+
+## Installation
+
+### Installing from MELPA
+
+`splunk-mode` is available on MELPA (as of [melpa/melpa#9005](https://github.com/melpa/melpa/pull/9005)).  Using MELPA to install `splunk-mode` is the recommended way to use this package.  You will need to:
+  1. [Enable the MELPA repository](https://melpa.org/#/getting-started)
+  2. Enable the package by adding the following lines to your Emacs init file (e.g., `~/.emacs`):
+
+    ```elisp
+    (package-install 'splunk-mode)
+    (require 'splunk-mode)
+    ```
+
+### Installing from Source
+
+To get the latest version of `splunk-mode`, clone this repository and then use:
+```elisp
+(add-to-list 'load-path "<path to splunk mode>")
+(require 'splunk-mode)
+```