Troubleshooting Guide / FAQ

[bobstrecansky]

Is your feature request related to a problem?

@agoallikmaa mentioned that he has helped people set up the opentelemetry-php package in their specific environments. When doing so, the consumers of the library have run into some similar pitfalls.

Describe the solution you'd like
We'd like to create a FAQ / Troubleshooting document. This may have some crossover with the library documentation, but it might be helpful for new contributors to ensure that they are performing all of the things they need to do to get the library working.