readme: document most important CMake options

[muzarski]

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• PR description sums up the changes and reasons why they should be introduced.
• I have implemented Rust unit tests for the features/changes introduced.
• I have enabled appropriate tests in .github/workflows/build.yml in gtest_filter.
• I have enabled appropriate tests in .github/workflows/cassandra.yml in gtest_filter.

[wprzytula]

❓ Can you confirm that the following builds a static driver library (no shared) in release mode and links it against integration tests?

mkdir build
cd build
cmake -DCASS_BUILD_SHARED=OFF -DCASS_BUILD_INTEGRATION_TESTS=ON -DCASS_USE_STATIC_LIBS=ON -DCMAKE_BUILD_TYPE=Release ..
make

[wprzytula]

If so, let's add this as another example.

[muzarski]

Well, just by looking at the command I would confirm. However, when I checked by running it - it does not work.. It's because it does not work even with just -DCASS_BUILD_SHARED=OFF in general..

The error:

CMake Error at scylla-rust-wrapper/CMakeLists.txt:16 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_FILE:scylla_cpp_driver_shared>

  No target "scylla_cpp_driver_shared"
Call Stack (most recent call first):
  scylla-rust-wrapper/CMakeLists.txt:52 (create_copy)


CMake Error at scylla-rust-wrapper/CMakeLists.txt:16 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_FILE:scylla_cpp_driver_shared>

  No target "scylla_cpp_driver_shared"
Call Stack (most recent call first):
  scylla-rust-wrapper/CMakeLists.txt:52 (create_copy)


CMake Error at scylla-rust-wrapper/CMakeLists.txt:16 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_FILE:scylla_cpp_driver_shared>

  No target "scylla_cpp_driver_shared"
Call Stack (most recent call first):
  scylla-rust-wrapper/CMakeLists.txt:52 (create_copy)


CMake Error at scylla-rust-wrapper/CMakeLists.txt:16 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_FILE:scylla_cpp_driver_shared>

  No target "scylla_cpp_driver_shared"
Call Stack (most recent call first):
  scylla-rust-wrapper/CMakeLists.txt:52 (create_copy)

This needs to be investigated. I'll open an issue.

However, if you execute the command you provided while removing -DCASS_BUILD_SHARED_LIBS=OFF, it works as expected - it builds integration tests library linked against static driver library. The only difference is that shared library is still being built.

[wprzytula]

Merging this one. If the issue upon build with shared lib turned off is not solved soon, I'll mention it in MAINTENANCE.md in a separate PR.