Consolidate duplicate content in touristic-autism tutorial series

[lemonade-37]

Remove duplicate intro text in touristic-autism guides

Problem

The same intro paragraph appears in 10 touristic-autism_*.md files:

"The basic guides that have been merged and adapted are the [Ruby on Rails Tutorial]..."

Solution

Create a shared include file and replace duplicates with {% include touristic-autism-intro.md %}.

Files to update

• touristic-autism_basic-app.md
• touristic-autism_continuous-deployment.md
• touristic-autism_design.md
• touristic-autism_git.md
• touristic-autism_google-map.md
• touristic-autism_image-upload.md
• touristic-autism_intro.md
• touristic-autism_resource-modeling.md
• touristic-autism_resource-rating.md
• touristic-autism_static-pages-tdd.md