README: tech document and twitter account

README.md

@@ -8,6 +8,7 @@ Oxigraph
 [![actions status](https://github.com/oxigraph/oxigraph/workflows/build/badge.svg)](https://github.com/oxigraph/oxigraph/actions)
 [![dependency status](https://deps.rs/repo/github/oxigraph/oxigraph/status.svg)](https://deps.rs/repo/github/oxigraph/oxigraph)
 [![Gitter](https://badges.gitter.im/oxigraph/community.svg)](https://gitter.im/oxigraph/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+[![Twitter URL](https://img.shields.io/twitter/url?style=social&url=https%3A%2F%2Ftwitter.com%2Foxigraph)](https://twitter.com/oxigraph)
 
 Oxigraph is a graph database implementing the [SPARQL](https://www.w3.org/TR/sparql11-overview/) standard.
 
@@ -33,7 +34,7 @@ Oxigraph implements the following specifications:
 * [Turtle](https://www.w3.org/TR/turtle/), [TriG](https://www.w3.org/TR/trig/), [N-Triples](https://www.w3.org/TR/n-triples/), [N-Quads](https://www.w3.org/TR/n-quads/), and [RDF XML](https://www.w3.org/TR/rdf-syntax-grammar/) RDF serialization formats for both data ingestion and retrieval using the [Rio library](https://github.com/oxigraph/rio).
 * [SPARQL Query Results XML Format](http://www.w3.org/TR/rdf-sparql-XMLres/), [SPARQL 1.1 Query Results JSON Format](https://www.w3.org/TR/sparql11-results-json/) and [SPARQL 1.1 Query Results CSV and TSV Formats](https://www.w3.org/TR/sparql11-results-csv-tsv/).
 
-A preliminary benchmark [is provided](bench/README.md).
+A preliminary benchmark [is provided](bench/README.md). There is also [a document describing Oxigraph technical architecture](https://github.com/oxigraph/oxigraph/wiki/Architecture).
 
 
 ## License