WIP: Add long-term vision doc and basic info to README (#9)

* Add long-term vision doc

I have been recently thinking about what should be the long-term vision for OpenTelemetry Agent/Collector. I believe it is important to have a clearly articulated set of high-level goals and guiding principles for the product that we work on. I took a first stab at it and would highly appreciate feedback on it and whether you think it is aligned with the goals of the OpenTelemetry community.

This has been already circulated internally at Omnition and also in Gitter channel https://gitter.im/open-telemetry/community

* Fix PR comments.

README.md

@@ -1,2 +1,8 @@
-# opentelemetry service
-OpenTelemetry service
+# OpenTelemetry Service
+The OpenTelemetry service is a set of components that can collect traces, metrics and eventually other telemetry data (e.g. logs) from processes instrumented by OpenTelementry or other monitoring/tracing libraries (Jaeger, Prometheus, etc.), do aggregation and smart sampling, and export traces and metrics to one or more monitoring/tracing backends. The service will allow to enrich and transform collected telemetry (e.g. add additional attributes or scrab personal information).
+
+The OpenTelemetry service has two primary modes of operation: Agent (a locally running daemon) and Collector (a standalone running service).
+
+## Vision
+
+We have a long-term vision for OpenTelemetry Agent that guides us and helps to decide what features we implement and what the priorities are. See [docs/VISION.md](docs/VISION.md).

docs/VISION.md

@@ -0,0 +1,23 @@
+# OpenTelemetry Service Long-term Vision
+
+The following are high-level items that define our long-term vision for OpenTelemetry Service, what we aspire to achieve. This vision is our daily guidance when we design new features and make changes to the Service.
+
+This is a living document that is expected to evolve over time.
+
+## Performant
+Highly stable and performant under varying loads. Well-behaved under extreme load, with predictable, low resource consumption.
+
+## Observable
+Expose own operational metrics in a clear way. Be an exemplar of observable service. Allow configuring the level of observability (more or less metrics, traces, logs, etc reported).
+
+## Multi-Data
+Support traces, metrics, logs and other relevant data types.
+
+## Usable Out of the Box
+Reasonable default configuration, supports popular protocols, runs and collects out of the box.
+
+## Extensible
+Extensible and customizable without touching the core code. Can create custom agents based on the core and extend with own components. Welcoming 3rd party contribution policy.
+
+## Unified Codebase
+One codebase for daemon (Agent) and standalone service (Collector).