Update Readme file with API language

[skonkiel]

The free Altmetric API (and thus rAltmetric) can be used without a key, but our API is only meant to be used that way for small-scale, noncommercial analyses.

To help rAltmetric users understand how to request an API key for larger scale analyses and commercial uses (eg reporting) and to point people towards the Altmetric help documentation when they have data-related questions, it would be wonderful to have the README.md file updated with the following language:

This package provides a way to programmatically retrieve metrics from various publication types (books, journal articles, data sets, and more) from Altmetric. The package is really simple to use and only has two major functions:

• altmetrics - Pass it a doi, isbn, uri, arxiv id or other to get metrics
• altmetric_data - Pass it the results from the previous call to get a tidy data.frame

rAltmetric uses the free Altmetric API to retrieve metrics. You can use this package without an API key for small-scale or exploratory noncommercial analyses.

You’ll need to provide rAltmetric with an Altmetric API key to avoid rate limits if:

• You intend to retrieve data for more than 250 publications, or
• You intend to use this package for any kind of commercial analyses (including organizational reporting, consulting work, etc)

To request an Altmetric API key, email info@altmetric.com with a description of your project.

Package-related questions, feature requests and issues should go here.

Altmetric data-related questions can usually be answered by checking out their API documentation or Altmetric support portal or, if all else fails, emailing support@altmetric.com.

[skonkiel]

I almost forgot the other thing: it would be great to have the newer Altmetric logo added to replace the old donut that's currently there. Thanks!