docs: Update readme to reflect tracing feature is needed for read-table

[OussamaSaoudi-db]

What changes are proposed in this pull request?

Updates the docs to reflect that tracing is required to be enabled in the read_table.c example code.

How was this change tested?

Compiling without the tracing feature yields the following error:

Undefined symbols for architecture arm64:
  "_enable_event_tracing", referenced from:
      _main in read_table.c.o

And compiling with it works.

[OussamaSaoudi-db]

The error comes from this line in read_table.c.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.46%. Comparing base (12020d8) to head (86f70c8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #619   +/-   ##
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  Coverage   83.46%   83.46%           
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  Files          75       75           
  Lines       16918    16918           
  Branches    16918    16918           
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  Hits        14120    14120           
  Misses       2143     2143           
  Partials      655      655           

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[nicklan]

ugg this is a bit of a mess. thanks for noticing this. So, default-engine is a "default" feature in the ffi crate. So you'd have to do --no-default-features to not get it, and then read-table would break.

So probably just update the docs to specify that you should enable the tracing feature and remove any mention of the default-engine one for now.

@zachschuermann, let's add this to the list of things we need to fix when we look at feature flags again.

[zachschuermann]

opened an issue for all our feature flag woes #642

[zachschuermann]

lgtm