Add example initializer to be copied to projects

[glensc]

Perhaps we still need some file to be added to auto_prepend_file config.

Fixes: #42

[glensc]

@perftools/maintainers: Should this example file be complete with all configuration options? or should this file be minimal and pointing to documentation?

a fine balance between maintainability (duplication) and usability for the end-users.

In other words, should we but more effort into having good defaults, or rather have it copied out every bit that can be configured.

[markstory]

Should this example file be complete with all configuration options? or should this file be minimal and pointing to documentation?

I would do all configuration and include the documentation in the example file. Then the docs could link to the current source file.

[glensc]

There's also defaults in the source itself:

• https://github.com/perftools/php-profiler/blob/0.14.0/src/Profiler.php#L269-L292

[glensc]

Updated, something like this then?

[glensc]

There's still duplication in readme file, becase moving them to one big file made imho it unreadable