1. I followed the description for the Cmake-setup and noticed in the example CMakeList.txt shown at the end of https://docs.seqan.de/seqan/3-master-user/setup.html that compiler optimization options such as -O3 is missing, which will lead to poor performance for users who do not recognize it.
   I now use
   ```cmake
   add_compile_options(-DNDEBUG -Wall -Wextra -Wunused-parameter -Wunused-variable -pedantic -Werror -O3)
   ```
   
   
   in CmakeLists.txt.

Thank you for pointing this out. It is a known fact / best practice in the CMake community that -DCMAKE_BUILD_TYPE=Release must be specified to enable optimized builds, e.g. cmake -DCMAKE_BUILD_TYPE=Release <seqan3-source-path> , but since our documentations should be accessible for "new" C++ programmers or "new" CMake users, we should add a section that teaches how to enable Release builds.

The best-practice in CMake for header-only libraries, like SeqAn2 or SeqAn3, is to specify only the minimal required flags that are needed to compile any given source that uses SeqAn. Additional flags, like hardening options or performance options is up to the application developer and/or package maintainer. The rational is simple, if we would add the -O3 flag to our cmake export, no-one could do a debug-build any more, because we then would dictate you to always have the -O3 flag in your Makefile.

2\. The cmake-setup specifies that one has to call
    cmake ../source -DCMAKE_CXX_COMPILER=/path/to/executable/g++-7
    The help pages of cmake version 3.16.3 on macOS and cmake version 3.10.2 on Linux state that options come before arguments, but only the macOS version enforces this. So on my macOS system only
    ```shell
    cmake  -DCMAKE_CXX_COMPILER=/path/to/executable/g++-7 ../source
    ```
    
    
    works. To simplify the use for macOS, it is probably better use this order in the cmake-setup section (and elsewhere) which works on both platforms.

Thank you for this, too :)