maint: Update README with latest OTel SDK version (#375)

## Which problem is this PR solving?
Updates the OTel SDK version the distro is built with and adds a note
about why we've pinned to 1.6.0 with link to our migration guide.

- Closes #374

## Short description of the changes
- Update README with latest OTel SDK version
- Add note around HTTP semantic versions with link to docs

.gitignore

@@ -457,4 +457,7 @@ $RECYCLE.BIN/
 smoke-tests/collector/data.json
 smoke-tests/collector/data-results/*.json
 smoke-tests/report.xml
-smoke-tests/report.html
+smoke-tests/report.html
+
+# asdf local tools versions file
+.tool-versions

README.md

@@ -10,7 +10,13 @@ It makes getting started with OpenTelemetry and Honeycomb easier!
 
 Latest release built with:
 
-- [OpenTelemetry Version 1.4.0](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.4.0)
+- [OpenTelemetry Version 1.6.0](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.6.0)
+
+***NOTE***
+
+OpenTelemetry .NET SDK versions after 1.6.0 use updated HTTP semantic conventions that result in different telemetry attribute keys and can contribute to unexpected query results in Honeycomb. For this reason, we have decided the Honeycomb OpenTelemetry distro will not take further updates yet.
+
+Please see our [Migration guide for HTTP semantic conventions](https://docs.honeycomb.io/troubleshoot/product-lifecycle/recommended-migrations/#migrate-to-stabilized-opentelemetry-semantic-conventions) for more details.
 
 ## Getting Started