add changelog

Author: etpinard

CHANGELOG.md

@@ -0,0 +1,21 @@
+# Orca changelog
+
+For more context information, please read through the
+[release notes](https://github.com/plotly/orca/releases).
+
+To see all merged commits on the master branch that will be part of the next Orca release, go to:
+
+https://github.com/plotly/orca/compare/vX.Y.Z...master
+
+where X.Y.Z is the semver of most recent Orca release.
+
+
+## [1.0.0] 2018-05-17
+
+First Orca release :tada:
+
+See installation instructions
+[here](https://github.com/plotly/orca#installation). This release ships with
+Orca CLI command `graph` (for plotly.js graph exports) and `serve` (which boots
+up a server similar to Plotly's Image Server). Run `orca graph --help` and `orce
+serve --help` for more info.