Enhance the BETA description

[pellared]

Per: https://splunk.slack.com/archives/CQ17ZQJFP/p1618450029204900

I propose to change the following block:

🚧 This project is currently in BETA.

Into:

🚧 This project is currently in BETA. It is officially supported by Splunk. However, breaking changes MAY be introduced.

At least in the repos that already have been released such us:

• https://github.com/signalfx/splunk-otel-collector
• https://github.com/signalfx/splunk-otel-collector-chart
• https://github.com/signalfx/splunk-otel-js-web
• https://github.com/signalfx/splunk-otel-python
• https://github.com/signalfx/splunk-otel-js
• https://github.com/signalfx/splunk-otel-java-lambda
• https://github.com/signalfx/splunk-otel-java

[flands]

@pellared see https://github.com/signalfx/splunk-otel-collector which currently states:

🚧 This project is currently in BETA (what does beta mean?)

Which links to: https://github.com/signalfx/splunk-otel-collector/blob/main/docs/beta-definition.md

Do you think this is sufficient?

[pellared]

Of course. I have intentionally not created any PR in this repo