docs/INSTALL.md: minor formatting fixes

The configure script always tries to find a working SSL library unless

explicitly told not to. If you have OpenSSL installed in the default search

path for your compiler/linker, you don't need to do anything special. If you

have OpenSSL installed in /usr/local/ssl, you can run configure like:

have OpenSSL installed in `/usr/local/ssl`, you can run configure like:

    ./configure --with-ssl

If you have OpenSSL installed somewhere else (for example, /opt/OpenSSL) and

If you have OpenSSL installed somewhere else (for example, `/opt/OpenSSL`) and

you have pkg-config installed, set the pkg-config path first, like this:

    env PKG_CONFIG_PATH=/opt/OpenSSL/lib/pkgconfig ./configure --with-ssl