update README for sudo make install

[claresinger]

the sudo make install step no longer puts cmake files in the share/libcloudph++ directory rather in lib/cmake/libclouph++ so the following line of the documentation should be updated to avoid confusion:

This will copy the libcloudph++ headers into the system include path (e.g. /usr/include/libcloudph++), copy the libcloudph++-config.cmake file into the system share directory (e.g. /usr/share/libcloudph++) and install the shared library file (e.g. /usr/lib).

[trontrytel]

Will be fixed by pull #377