There’s been an excellent free solution for documenting SSAS metadata in multi-dimensional models for quite some time: http://www.purplefrogsystems.com/blog/2010/09/olap-cube-documentation-in-ssrs-part-1/.
I had the opportunity recently at a client to implement a version of this report solution rewritten for SSAS tabular. It took a few tweaks to the DMV queries, but I eventually got it to meet my needs. I’m sharing the source files here for those that might be in need: http://ow.ly/xYaJ3005IHu
Please try it out and let me know how it works for you.
A huge thank you to Alex Whittles for the vast bulk of this base code!