documentation: incorrect instructions given

The instructions don't work as given
There is no need to make or change into the build directory

```-DDEBUG_LOG=OFF -DCOVERAGE=OFF -CMAKE_BUILD_TYPE=Release```

should be ```-DCMAKE_BUILD_TYPE```

This does work:

```
$ cmake -B build -DDEBUG_LOG=OFF -DCOVERAGE=OFF -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_BUILD_TYPE=Release
-- Clang detected.
-- Configuring done (0.1s)
-- Generating done (0.0s)
-- Build files have been written to zlib-accel/build

$ cmake --build build -j"$(nproc)"
[ 25%] Building CXX object CMakeFiles/zlib-accel.dir/config/config_reader.cpp.o
[ 25%] Building CXX object CMakeFiles/zlib-accel.dir/config/config.cpp.o
[ 37%] Building CXX object CMakeFiles/zlib-accel.dir/zlib_accel.cpp.o
[ 50%] Building CXX object CMakeFiles/zlib-accel.dir/iaa.cpp.o
[ 62%] Building CXX object CMakeFiles/zlib-accel.dir/qat.cpp.o
[ 75%] Building CXX object CMakeFiles/zlib-accel.dir/utils.cpp.o
[ 87%] Building CXX object CMakeFiles/zlib-accel.dir/statistics.cpp.o
[100%] Linking CXX shared library libzlib-accel.so
[100%] Built target zlib-accel

$ cmake --install build
-- Install configuration: "Release"
```

```cmake -B build -DDEBUG_LOG=OFF -DCOVERAGE=OFF -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_BUILD_TYPE=Release -DUSE_QAT=ON``` works too.

Please proofread and test the instructions more carefully.