Provide EODash documentation

[KathiSchleidt]

Under #77 we've clarified that it is possible to display data coming from rasdaman WCS via EODash. However, all the documentation provided there was external. At least basic information should be available from the FAIRiCUBE RTD pages. In addition to integrating data from rasdaman WCS should also mention other sources, e.g. S3 buckets, Sentinel-Hub services.