add transaction protocol notes

Author: AbhiPrasad

src/docs/sdk/performance/opentelemetry/index.mdx

@@ -22,12 +22,14 @@ TODO: Add history about OpenTelemetry Sentry Exporter: https://github.com/open-t
 
 TODO: Talk about the approach we are using, based on Matt's hackweek project - https://github.com/getsentry/sentry-ruby/pull/1876
 
-## Transaction Protocol
-
-TODO: Talk about generating transactions
+## Span Protocol
 
 import "./span-protocol.mdx"
 
+## Transaction Protocol
+
+There is no concept of a transaction within OpenTelemetry, so we rely on promoting spans to become transactions. The span `description` becomes the transaction `name`, and the span `op` becomes the transaction `op`. Therefore, OpenTelemetry spans must be mapped to Sentry spans before they can be promoted to become a transaction.
+
 ## OpenTelemetry Context
 
 Aside from information from Spans and Transactions, OpenTelemetry has meta-level information about the SDK, resource, and service that generated spans. To track this information, we generate a new OpenTelemetry Event Context.

src/docs/sdk/performance/opentelemetry/span-protocol.mdx

@@ -1,5 +1,3 @@
-## Span Protocol
-
 Below describe the transformations between an OpenTelemetry span and a Sentry Span. Related: [the interface for a Sentry Span](https://develop.sentry.dev/sdk/event-payloads/span/), [the Relay spec for a Sentry Span](https://github.com/getsentry/relay/blob/master/relay-general/src/protocol/span.rs) and the spec for an [OpenTelemetry span](https://github.com/open-telemetry/opentelemetry-proto/blob/724e427879e3d2bae2edc0218fff06e37b9eb46e/opentelemetry/proto/trace/v1/trace.proto#L80-L256).
 
 This is based on a mapping done as part of work on the [OpenTelemetry Sentry Exporter](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/exporter/sentryexporter/docs/transformation.md).
@@ -282,6 +280,8 @@ This is based on a mapping done as part of work on the [OpenTelemetry Sentry Exp
     </tbody>
 </table>
 
+Currently there is no spec for how [Span.link in OpenTelemetry](https://github.com/open-telemetry/opentelemetry-proto/blob/724e427879e3d2bae2edc0218fff06e37b9eb46e/opentelemetry/proto/trace/v1/trace.proto#L220-L247) should appear in Sentry.
+
 ### Span Status
 
 In OpenTelemetry, [Span Status is an enum of 3 values](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/api.md#set-status), while [Sentry's Span Status is an enum of 17 values](https://github.com/getsentry/relay/blob/ed3a521f773ecd4bf9a2aefd7af80080d56d0841/relay-common/src/constants.rs#L200-L286) that map to the [GRPC status codes](https://github.com/grpc/grpc/blob/master/doc/statuscodes.md). Each of the Sentry Span Status codes also map to HTTP codes. Sentry adopted it's Span Status spec from OpenTelemetry, [who used the GRPC status code spec](https://github.com/open-telemetry/opentelemetry-specification/blob/8fb6c14e4709e75a9aaa64b0dbbdf02a6067682a/specification/api-tracing.md#status), but later on changed to the current spec it uses today.