Stackdriver log correlation: Improve description of library stability. (#1406)
Stackdriver log correlation: Improve description of library stability. (#1406)

This change is similar to a change made to Log4j log correlation: https://github.com/census-instrumentation/opencensus-java/pull/1402#discussion_r213934235
census-instrumentation/opencensus-java,sebright/instrumentation-java,songy23/instrumentation-java,bogdandrutu/instrumentation-java,bogdandrutu/opencensus-java,songy23/instrumentation-java,census-instrumentation/opencensus-java,sebright/instrumentation-java,sebright/opencensus-java,songy23/instrumentation-java,bogdandrutu/instrumentation-java,census-instrumentation/opencensus-java,bogdandrutu/opencensus-java,bogdandrutu/opencensus-java,sebright/opencensus-java,sebright/opencensus-java