sdk/log: Document how Processor and Exporter interfaces can be extend…

…ed (#5347)

CONTRIBUTING.md

@@ -570,6 +570,9 @@ functionality should be added, each one will need their own super-set
 interfaces and will duplicate the pattern. For this reason, the simple targeted
 interface that defines the specific functionality should be preferred.
 
+See also:
+[Keeping Your Modules Compatible: Working with interfaces](https://go.dev/blog/module-compatibility#working-with-interfaces).
+
 ### Testing
 
 The tests should never leak goroutines.

sdk/log/DESIGN.md

@@ -50,6 +50,11 @@ The user set processors for the `LoggerProvider` using
 
 The user can configure custom processors and decorate built-in processors.
 
+The specification may add new operations to the
+[LogRecordProcessor](https://opentelemetry.io/docs/specs/otel/logs/sdk/#logrecordprocessor).
+If it happens, [CONTRIBUTING.md](../../CONTRIBUTING.md#how-to-change-other-interfaces)
+describes how the SDK can be extended in a backwards-compatible way.
+
 ### SimpleProcessor
 
 The [Simple processor](https://opentelemetry.io/docs/specs/otel/logs/sdk/#simple-processor)
@@ -74,6 +79,11 @@ so that the caller can reuse the passed slice
 (e.g. using [`sync.Pool`](https://pkg.go.dev/sync#Pool))
 to avoid heap allocations on each call.
 
+The specification may add new operations to the
+[LogRecordExporter](https://opentelemetry.io/docs/specs/otel/logs/sdk/#logrecordexporter).
+If it happens, [CONTRIBUTING.md](../../CONTRIBUTING.md#how-to-change-other-interfaces)
+describes how the SDK can be extended in a backwards-compatible way.
+
 ### Record
 
 The [ReadWriteLogRecord](https://opentelemetry.io/docs/specs/otel/logs/sdk/#readwritelogrecord)