Migrating to Conan

It would be nice to have a section in HOWTO's about how to migrate an existing project to Conan.

One of the biggest issues I faced was how to get versions of libraries that are already being used into Conan and use them. Many of the Conan documents assume you're starting from scratch and making a new library which is not the case when migrating and it seems the learning curve with current documentation for doing this is rather steep.

For example when trying to compile `cmake 3.5.2`, I felt I needed to follow this article. https://docs.conan.io/en/latest/creating_packages/existing_binaries.html

After I compiled cmake, I currently don't feel familiar enough with conan to write this myself.