[cpp] Install command for libz on Ubuntu to README.
[cpp] Install command for libz on Ubuntu to README.

mikeb01/Aeron,EvilMcJerkface/Aeron,mikeb01/Aeron,oleksiyp/Aeron,galderz/Aeron,oleksiyp/Aeron,real-logic/Aeron,real-logic/Aeron,real-logic/Aeron,EvilMcJerkface/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,EvilMcJerkface/Aeron,galderz/Aeron,real-logic/Aeron,galderz/Aeron,galderz/Aeron,oleksiyp/Aeron,mikeb01/Aeron