Create README.md for the ot bridge (#2896)

* Create README.md

Some very bare-bones introductory documentation on how to use the ot bridge

* Update README.md

linting

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more linting

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

bridge/opentracing/README.md

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+# OpenTelemetry/OpenTracing Bridge
+
+## Getting started
+
+`go get go.opentelemetry.io/otel/bridge/opentracing`
+
+Assuming you have configured an OpenTelemetry `TracerProvider`, these will be the steps to follow to wire up the bridge:
+
+```go
+import (
+	"go.opentelemetry.io/otel"
+	otelBridge "go.opentelemetry.io/otel/bridge/opentracing"
+)
+
+func main() {
+	/* Create tracerProvider and configure OpenTelemetry ... */
+
+	otelTracer := tracerProvider.Tracer("tracer_name")
+	// Use the bridgeTracer as your OpenTracing tracer.
+	bridgeTracer, wrapperTracerProvider := otelBridge.NewTracerPair(otelTracer)
+	// Set the wrapperTracerProvider as the global OpenTelemetry
+	// TracerProvider so instrumentation will use it by default.
+	otel.SetTracerProvider(wrapperTracerProvider)
+
+	/* ... */
+}
+```
+
+## Interop from trace context from OpenTracing to OpenTelemetry
+
+In order to get OpenTracing spans properly into the OpenTelemetry context, so they can be propagated (both internally, and externally), you will need to explicitly use the `BridgeTracer` for creating your OpenTracing spans, rather than a bare OpenTracing `Tracer` instance.
+
+When you have started an OpenTracing Span, make sure the OpenTelemetry knows about it like this:
+
+```go
+	ctxWithOTSpan := opentracing.ContextWithSpan(ctx, otSpan)
+	ctxWithOTAndOTelSpan := bridgeTracer.ContextWithSpanHook(ctxWithOTSpan, otSpan)
+	// Propagate the otSpan to both OpenTracing and OpenTelemetry
+	// instrumentation by using the ctxWithOTAndOTelSpan context.
+```