Clarify installation of CLI and library in `README`#8

JR-1991 wants to merge 2 commits intomastergdcc/rust-dataverse:masterfrom

6-clarification-for-the-cargotoml-section-of-readmes-installation-proceduregdcc/rust-dataverse:6-clarification-for-the-cargotoml-section-of-readmes-installation-procedureCopy head branch name to clipboard