message: Add a description of the GINKGO_VERBOSE_LEVEL option in the README
diff: @@ -90,6 +90,9 @@ Ginkgo adds the following additional switches to control what is being built:
  errors due to ABI incompatibilities. The default is `OFF`.
  * `-DCMAKE_INSTALL_PREFIX=path` sets the installation path for `make install`.
  The default value is usually something like `/usr/local`
  +* `-DGINKGO_VERBOSE_LEVEL=integer` sets the verbosity of Ginkgo.
  + * `0` disables all output in the main libraries,
  + * `1` enables a few important messages related to unexpected behavior (default).
  * `-DCUDA_ARCHITECTURES=<list>` where `<list>` is a semicolon (`;`) separated
  list of architectures. Supported values are:
  