Rename index, fix install TOC

Author: lonnieezell

docs/_index.md docs/index.mddocs/_index.md renamed to docs/index.md

@@ -1,6 +1,7 @@
 # Installation
 
 - [Installation](#installation)
+    - [Troubleshooting](#troubleshooting)
       - [IMPORTANT: composer error](#important-composer-error)
       - [Note: migration error](#note-migration-error)
   - [Initial Setup](#initial-setup)
@@ -20,6 +21,8 @@ If you have it installed as a phar, or othewise you will need to adjust the way
 
 ---
 
+### Troubleshooting
+
 #### IMPORTANT: composer error
 
 If you get the following error: