RFR: Adding troubleshooting section to README.md

[Adam Sotona]

Hi,
based on an external contributor recent experience with javac benchmarking javac using jmh-jdk-microbenchmarks I've created a troubleshooting section of the README.md

Thanks,
Adam

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Commit messages:
 - Added troubleshooting section to README.md

Changes: https://git.openjdk.java.net/jmh-jdk-microbenchmarks/pull/5/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmh-jdk-microbenchmarks&pr=5&range=00
  Stats: 41 lines in 1 file changed: 41 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmh-jdk-microbenchmarks/pull/5.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh-jdk-microbenchmarks pull/5/head:pull/5

PR: https://git.openjdk.java.net/jmh-jdk-microbenchmarks/pull/5