doc: updated docs and references

- reference docs: spec and command-line tool
- contributing
- updated readme

Change-Id: I908120f929f0a6b15b0a568de5118e53dfdab659
diff --git a/README.md b/README.md
index b6733f5..280c985 100644
--- a/README.md
+++ b/README.md
@@ -13,10 +13,11 @@
 aimed at improving the overall experience of putting
 configurations to good use.
 
-Features highlights:
+Some highlights:
 
 - JSON superset: get started quickly
 - convert existing YAML and JSON
+- arbitrary-precision arithmetic
 - reformatter
 - automatically simplify configurations
 - powerful scripting