Add Additional Hyperlinks to README.md

[Krieke]

Section: https://github.com/SEMICeu/LinkedDataEventStreams#the-linked-data-event-streams-specification:

• First alinea: create a hyperlink on RDF to https://www.w3.org/RDF/
• Fourth alinea: create hyperlinks on Activity Streams to https://www.w3.org/TR/activitystreams-core/, on DCAT-AP to https://joinup.ec.europa.eu/collection/semantic-interoperability-community-semic/solution/dcat-application-profile-data-portals-europe, on LDP to https://www.w3.org/TR/ldp/ or Shape Trees to https://shapetrees.org/.

Section: https://github.com/SEMICeu/LinkedDataEventStreams#build-the-spec :

• create a hyperlink on bikeshed to the bikeshed documentation GitHub pages link https://tabatkins.github.io/bikeshed/

Section: https://github.com/SEMICeu/LinkedDataEventStreams#acknowledgements

• create a hyperlink on SEMIC to https://joinup.ec.europa.eu/collection/semantic-interoperability-community-semic

[pietercolpaert]

Fixed in https://github.com/SEMICeu/LinkedDataEventStreams/commit/363942d49428b101f433f9371de4bdbc920cea0a