Discord badge added (#5748)
Discord badge added (#5748)

## What is the goal of this PR?

Slack badge changed to discord badge

graknlabs/grakn,graknlabs/grakn,graknlabs/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn,lolski/grakn,lolski/grakn