(Docs)fix wrong commands of enabling SSL/TLS support

[Risc-lt]

In the SSL/TLS support part, the current readme says to run make USE_SSL=1 to build and install files related to hiredis_ssl. However, after running it, the system does not install the libhiredis_ssl correctly.

This is due to the option here in CMakeLists.txt is set to OFF as default but make USE_SSL=1 does not enable it.

OPTION(ENABLE_SSL "Build hiredis_ssl for SSL support" OFF)

This is the result of just running make USE_SSL=1 and sudo make install

mkdir -p /usr/local/include/hiredis /usr/local/include/hiredis/adapters /usr/local/lib
cp -pPR hiredis.h async.h read.h sds.h alloc.h sockcompat.h /usr/local/include/hiredis
cp -pPR adapters/*.h /usr/local/include/hiredis/adapters
cp -pPR libhiredis.so /usr/local/lib/libhiredis.so.1.2.1-dev
cd /usr/local/lib && ln -sf libhiredis.so.1.2.1-dev libhiredis.so && ln -sf libhiredis.so.1.2.1-dev libhiredis.so.1
cp -pPR libhiredis.a /usr/local/lib
mkdir -p /usr/local/lib/pkgconfig
cp -pPR hiredis.pc /usr/local/lib/pkgconfig

This is the result of running cmake . -DENABLE_SSL=ON before the commands above.

[ 66%] Built target hiredis
[ 83%] Built target hiredis_ssl
[100%] Built target hiredis-test
Install the project...
-- Install configuration: ""
-- Installing: /usr/local/lib64/libhiredis.so.1.2.1-dev
-- Installing: /usr/local/lib64/libhiredis.so
-- Installing: /usr/local/build/native/hiredis.targets
-- Up-to-date: /usr/local/include/hiredis/hiredis.h
-- Up-to-date: /usr/local/include/hiredis/read.h
-- Up-to-date: /usr/local/include/hiredis/sds.h
-- Up-to-date: /usr/local/include/hiredis/async.h
-- Up-to-date: /usr/local/include/hiredis/alloc.h
-- Up-to-date: /usr/local/include/hiredis/sockcompat.h
-- Up-to-date: /usr/local/include/hiredis/adapters
-- Up-to-date: /usr/local/include/hiredis/adapters/macosx.h
-- Up-to-date: /usr/local/include/hiredis/adapters/ae.h
-- Up-to-date: /usr/local/include/hiredis/adapters/libev.h
-- Up-to-date: /usr/local/include/hiredis/adapters/libevent.h
-- Up-to-date: /usr/local/include/hiredis/adapters/poll.h
-- Up-to-date: /usr/local/include/hiredis/adapters/redismoduleapi.h
-- Up-to-date: /usr/local/include/hiredis/adapters/qt.h
-- Up-to-date: /usr/local/include/hiredis/adapters/libsdevent.h
-- Up-to-date: /usr/local/include/hiredis/adapters/glib.h
-- Up-to-date: /usr/local/include/hiredis/adapters/libhv.h
-- Up-to-date: /usr/local/include/hiredis/adapters/ivykis.h
-- Up-to-date: /usr/local/include/hiredis/adapters/libuv.h
-- Installing: /usr/local/lib64/pkgconfig/hiredis.pc
-- Installing: /usr/local/lib64/cmake/hiredis/hiredis-targets.cmake
-- Installing: /usr/local/lib64/cmake/hiredis/hiredis-targets-noconfig.cmake
-- Installing: /usr/local/lib64/cmake/hiredis/hiredis-config.cmake
-- Installing: /usr/local/lib64/cmake/hiredis/hiredis-config-version.cmake
-- Installing: /usr/local/lib64/libhiredis_ssl.so.1.2.1-dev
-- Installing: /usr/local/lib64/libhiredis_ssl.so
-- Installing: /usr/local/include/hiredis/hiredis_ssl.h
-- Installing: /usr/local/lib64/pkgconfig/hiredis_ssl.pc
-- Installing: /usr/local/lib64/cmake/hiredis_ssl/hiredis_ssl-targets.cmake
-- Installing: /usr/local/lib64/cmake/hiredis_ssl/hiredis_ssl-targets-noconfig.cmake
-- Installing: /usr/local/lib64/cmake/hiredis_ssl/hiredis_ssl-config.cmake

So it's obvious to see that files of libhiredis_ssl.so, hiredis_ssl.h and so on are left out and not installed correctly as expected. Thus I add the commands in the README.md to fix the problem since it's really hard to detect.