Improve manual installation

[nwneisen]

Discovered as part of https://mirantis.jira.com/browse/BOP-1286 There are manual installation steps at the end of the installation page: https://mirantis.github.io/mke-docs/docs/getting-started/install-mke-cli/#install-manually

There are a few things that we should improve with this

• After the binary is downloaded, we should provide steps to install it on the system. Typically this is done by copying the binary to /usr/local/bin/ but any folder in the users $PATH will work
• Most linux binaries are downloaded as non executable and require the user to run chmod +x <binary> before running them. I believe this is to give people warm fuzzies that it isn’t a malicious program that will just start running on their machine. We should follow the standard practice and modify our binaries this way and then add the command to make the binary executable to the manual steps.
• The last paragraph in this section is confusing. It reads as mkectl is self contained and has no dependencies, except it has these dependencies” We should reword it so it doesn’t contradict itself

The MKE CLI is a single binary that is capable of managing MKE clusters without any additional dependencies. Its use, though, requires that you have the following tools on your system:

[KoryKessel-Mirantis]

Hey @nwneisen. Please create a PR with rough/raw content that we can use to iterate-to-great.