Question for launching jekyll algolia

@pixelastic

## I got an error when launch the jekyll algolia, could you pls help to resolve it:

### What is the current behavior?

ALGOLIA_API_KEY='xxxx' bundle exec jekyll algolia
Configuration file: /Users/zhoupengfei/GitFolder/Test/docs/qingcloud-product-docs/_config.yml
Processing site...
Jekyll Feed: Generating feed for posts
Extracting records...
[✗ Error] No records found

The jekyll-algolia plugin could find any records to index

The plugin tried to extract records from the pages, posts and collections of
your site but could not find anything to index.

Make sure you did not exclude too many files from indexing using the
`files_to_exclude` option. You are currently excluding the following files:
index.html, index.markdown, index.mkdown, index.mkdn, index.mkd, index.md

Also double check that your current value for `nodes_to_index` can actually
match something in the pages. You are current indexing the following nodes:
p

Note that all the markup that is defined in the layouts won't be available
during extraction. Only the page content can be accessed. So if you defined
a layout markup that is used only for one page, you should move it to the
page instead.

### Git repository to reproduce the issue:

It's in internal gitlab...

### Ruby version used:

ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin17]

### Jekyll version used:

jekyll-3.8.5

Start by reviewing the project's _config.yml and the reported `bundle exec jekyll algolia` output, focusing on `files_to_exclude` and `nodes_to_index`. Reproduce with the stated Ruby and Jekyll versions if the internal repository can be made available; done means the command extracts records instead of reporting "No records found."

Written by the indexing model from the issue text.