Common FCA formats for formal contexts are missing

[itchy2385]

When using conexp-clj as a RESTful service, it is important to explain the standardized communication formats to the user. The communication formats are already specified to a certain extent in the REST API documentation. However, there is no comprehensive documentation. REST API documentation https://github.com/exot/conexp-clj/blob/dev/doc/REST-API-usage.md already refers to an introductory page on formats: https://github.com/exot/conexp-clj/blob/dev/doc/Common-FCA-File-Formats-for-Formal-Contexts. Unfortunately, this page is not available.

It would be helpful to add a page about common formats of formal contexts and provide a clear link to how these formats can be used based on the conexp-clj RESTful API.