draft a section on metadata standards

with reference to the N4M github

docs/_Research-Data-Management/03-md.md

@@ -25,12 +25,15 @@ For example: When you use your smartphone camera to take photos of your loved on
 6. Height of photograph
 
 # Metadata standards
-1. from general to more specific more microbiology? >other github page
-2. metadatastandards intro for microbiology: etc
 
-?? file type standards/ technical metadata
+Once a community agrees to a set of relevant metadata for their field, they can devise metadata standards.
+A metadata standard is usually defined for a given type of data and by different stakeholders (e.g., users community, data repositories).
+For every metadata fields part of a metadata standard, one could expect a human-readable description of the metadata field paired with a machine-readable persistent identifier of the field, then an indication of the level of requirements of this field in the standard and how many values of this field are expected (that is the cardinality).
 
 
+[More than a thousand standards are listed by the organisation `FAIRsharing.org`](https://fairsharing.org/search?fairsharingRegistry=Standard) which can be overwhelming.
+We compiled a [list of widely used metadata standards in the fied of microbiome research](https://github.com/NFDI4Microbiota/MetadataStandards)
+
 
 # Metadata management