Add more explanations and example snippets for commonly asked questions to Wiki

[richaber]

There are a lot of recurring support questions that we should probably just add explanations and snippets to the Wiki for.

For example, the difference between the searchable_posts index used by Search Page integrations, and the individual indices that can be enabled for Autocomplete in the WordPress Search Widget.

How to exclude individual posts from indexing.

How to exclude certain post types from indexing.

Etc.

[tw2113]

See https://github.com/WebDevStudios/algolia-snippet-library/