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

…le (#619)

## 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.

ffi/README.md

@@ -8,7 +8,7 @@ This crate provides a c foreign function internface (ffi) for delta-kernel-rs.
 You can build static and shared-libraries, as well as the include headers by simply running:
 
 ```sh
-cargo build [--release] [--features default-engine]
+cargo build [--release]
 ```
 
 This will place libraries in the root `target` dir (`../target/[debug,release]` from the directory containing this README), and headers in `../target/ffi-headers`. In that directory there will be a `delta_kernel_ffi.h` file, which is the C header, and a `delta_kernel_ffi.hpp` which is the C++ header.

ffi/examples/read-table/README.md

@@ -10,9 +10,9 @@ This example is built with [cmake]. Instructions below assume you start in the d
 Note that prior to building these examples you must build `delta_kernel_ffi` (see [the FFI readme] for details). TLDR:
 ```bash
 # from repo root
-$ cargo build -p delta_kernel_ffi [--release] [--features default-engine, tracing]
+$ cargo build -p delta_kernel_ffi [--release] --features tracing
 # from ffi/ dir
-$ cargo build [--release] [--features default-engine, tracing]
+$ cargo build [--release] --features tracing
 ```
 
 There are two configurations that can currently be configured in cmake: