Refactor GraphKB description in readme.md

[mathieulemieux]

GraphKB description in the readme.md file is hard to understand here:

pori_graphkb_api/README.md

Line 8 in cf5e35d

It is a graph database which is used to store variants, ontologies, and the relevance of this terms and variants. The KB uses strict controlled vocabulary to provide a parsable and machine-readable interface for other applications to build on. The API is a REST API built on node/express.

"It is a graph database which is used to store variants, ontologies, and the relevance of this terms and variants. The KB uses strict controlled vocabulary to provide a parsable and machine-readable interface for other applications to build on. The API is a REST API built on node/express."

Issue described here #44 (comment)
"something is wrong with this first sentence - this -> these possibly?"

Possible solution here: #44 (comment)
"What about this? :
It is a graph database which is used to store variants, ontologies, and statements about the relevance of these variants in a specific disease context. The knowledge base uses strict controlled vocabulary to provide a parsable and machine-readable interface for other applications to build on. The API is a REST API built on node/express."