Add explanation of the spec layout, etc. (#4)

README.md

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-# opentelemetry-specification
+# OpenTelemetry Specification
+
+![GitHub tag (latest SemVer)](https://img.shields.io/github/tag/open-telemetry/specification.svg) ![GitHub tag (latest SemVer pre-release)](https://img.shields.io/github/tag-pre/opentelemetry/specification.svg)
+
+* [Layout](#layout)
+  * [Terminology](#terminology)
+  * [Specification](#specification)
+  * [Semantic Conventions](#semantic-conventions)
+  * [Wire Protocol](#wire-protocol)
+* [Versioning](#versioning)
+* [Change Process](#change-process)
+* [License](#license)
+
+## Layout
+
+### [Terminology](./terminology.md)
+
+[terminology.md](./terminology.md) provides a glossary for languages commonly used throughout the OpenTelemetry project.
+
+### [Specification](./specification.md)
+
+[specification.md](./specification.md) is the versioned OpenTelemetry standard, explaining the cross-language requirements and expectations for implementations.
+
+### [Semantic Conventions](./semantic-conventions.md)
+
+[semantic-conventions.md](./semantic-conventions.md) describes conventional tags, log keys, etc. that should be used for common scenarios to ensure a consistent usage experience.
+
+## Versioning
+
+Changes to the content of the [specification](./specification.md) itself, including changes to [terminology](./terminology.md) and [semantic conventions](./semantic-conventions.md), are versioned according to [Semantic Versioning](https://semver.org/spec/v2.0.0.html) and described in [CHANGELOG.md](./changelog.md). Layout changes are not versioned. Specific implementations of the specification should specify which version they implement.
+
+Changes to the change process itself are not currently versioned but may be independently versioned in the future.
+
+## Change Process
+
+The change process is still evolving. For the short term, please use [issues](https://github.com/open-telemetry/specification/issues) to suggest changes and [pull requests](https://github.com/open-telemetry/specification/pulls) to suggest implementations of changes that have been discussed in a relevant issue.
+
+We will be setting up a more complete RFC process to streamline the discussion of changes.
+
+## License
+
+By contributing to OpenTelemetry Specification repository, you agree that your contributions will be licensed under its [Apache 2.0 License](https://github.com/open-telemetry/specification/blob/master/LICENSE).

semantic-conventions.md

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+# Semantic Conventions

specification.md

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+# Specification

terminology.md

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+# Terminology