[docs] add guidance around what a collector/distro is

docs/README.md

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+# OpenTelemetry Collector
+
+The OpenTelemetry Collector consists of the following components:
+
+* A mechanism that _MUST_ be able to load and parse an [OpenTelemetry Collector configuration
+  file](#configuration-file).
+* A mechanism that _MUST_ be able to include compatible
+  [Collector components](#opentelemetry-collector-components) that
+  the user wishes to include.
+
+These combined provide users the ability to easily switch between
+[OpenTelemetry Collector Distributions](#opentelemetry-collector-distribution) while also ensuring that components produced by
+the OpenTelemetry Collector SIG are able to work with any vendor who claims
+support for an OpenTelemetry Collector.
+
+## Configuration file
+
+An OpenTelemetry Collector configuration file is defined as YAML and _MUST_ support
+the following [minimum structure](https://pkg.go.dev/go.opentelemetry.io/collector/otelcol#Config):
+
+```yaml
+receivers:
+processors:
+exporters:
+connectors:
+extensions:
+service:
+  telemetry:
+  pipelines:
+```
+
+## OpenTelemetry Collector components
+
+For a library to be considered an OpenTelemetry Collector component, it _MUST_
+implement a [Component interface](https://pkg.go.dev/go.opentelemetry.io/collector/component#Component)
+defined by the OpenTelemetry Collector SIG.
+
+Components require a [unique identfier](https://pkg.go.dev/go.opentelemetry.io/collector/component#ID)
+to be included in an OpenTelemetry Collector. In the event of a name collision,
+the components resulting in the collision cannot be used simultaneously in a single OpenTelemetry
+Collector. In order to resolve this, the clashing components must use different identifiers.
+
+### Compatibility requirements
+
+A component is defined as compatible with an OpenTelemetry Collector when its dependencies are
+source- and version-compatible with the Component interfaces of that Collector.
+
+For example, a Collector derived from version tag v0.100.0 of the [OpenTelemetry Collector](https://github.com/open-telemetry/opentelemetry-collector) _MUST_ support all components that
+are version-compatible with the Golang Component API defined in the `github.com/open-telemetry/opentelemetry-collector/component` module found in that repository for that version tag.
+
+## OpenTelemetry Collector Distribution
+
+An OpenTelemetry Collector Distribution (Distro) is a compiled instance
+of an OpenTelemetry Collector with a specific set of components and features. A
+Distribution author _MAY_ choose to produce a distribution by utilizing tools
+and/or documentation supported by the OpenTelemetry project. Alternatively, a
+Distribution author _MUST_ provide end users with the capability for adding
+their own components to the Distribution's components. Note that the resulting
+binary from updating a Distribution to include new components
+is a different Distribution.