Add Contributing guide and add next as a dev dependency

CONTRIBUTING.md

@@ -0,0 +1,22 @@
+# Contributing
+
+This is living document describing how to contribute to SeqViz.
+
+## Development
+
+Before making or PR'ing changes, please set up and experiment with the demo application. Steps for doing that are described below.
+
+Install `seqviz` packages in the repository and repository's demo directories:
+
+```bash
+# seqviz
+npm i
+cd ./demo
+npm i
+```
+
+Start the demo application:
+
+```bash
+npm run start
+```