chore: fixing readme info (open-telemetry#2094)

Co-authored-by: Valentin Marchaud <contact@vmarchaud.fr>
Co-authored-by: Daniel Dyla <dyladan@users.noreply.github.com>

README.md

@@ -245,12 +245,10 @@ To request automatic tracing support for a module not on this list, please [file
 
 ## Upgrade guidelines
 
-### 0.19.0 to 1.0.0-rc.0
+### 0.18.x to 0.19.0
 
 - All plugins have been removed in favor of instrumentations.
-
-### 0.18.0 to 0.19.0
-
+
 - The `@opentelemetry/propagator-b3` package previously exported three propagators: `B3Propagator`,`B3SinglePropagator`, and `B3MultiPropagator`, but now only exports the `B3Propagator`. It extracts b3 context in single and multi-header encodings, and injects context using the single-header encoding by default, but can be configured to inject context using the multi-header endcoding during construction: `new B3Propagator({ injectEncoding: B3InjectEncoding.MULTI_HEADER })`. If you were previously using the `B3SinglePropagator` or `B3MultiPropagator` directly, you should update your code to use the `B3Propagator` with the appropriate configuration. See the [readme](./packages/opentelemetry-propagator-b3/readme.md) for full details and usage.
 
 ### 0.17.0 to 0.18.0