[Proposal] Incomplete installation guide - Add hint to install database schema

[hardcoding]

Description

I followed the steps under https://cartalyst.com/manual/sentinel/5.x#installation, but got an error (table 'users' missing) when trying to authenticate/register a user. Googling I found a hint to install database schema: https://stackoverflow.com/questions/40471120/database-setup-for-cartalyst-sentinel

Example

I would have liked a hint, that the database schema (located under vendor/cartalyst/sentinel/schema) could have to be manually created (via given sql-script).

[fineon]

Second this. I could do a PR to add some info to the docs for initial set-up guide