[enh] Add README

README.md

+# Install
+
+1. Clone:
+
+    git clone https://git.duniter.org/nodes/typescript/modules/gva-api
+    
+2. Compile (using NodeJS 9):
+
+    yarn
+    
+3. Start
+
+    node index.js direct_start --gva-host localhost
+    
+Then access GVA API at http://localhost:15000/graphql.
+    
+    
\ No newline at end of file