provide macOS and Linux installation via Homebrew and the datum-cloud homebrew tap

[scrivener221b]

We have an existing working example of installation of macOS binaries using Homebrew for the datumctl resource. It would be great if the install instructions for datum-mcp could be reduced to something simpler like those at https://github.com/datum-cloud/datumctl/blob/main/docs/user/installation.md#homebrew-macos . After this work would be done the docs could read as follows:

# Tap the Datum Cloud formula repository (only needs to be done once)
brew tap datum-cloud/homebrew-tap

# Install datumctl
brew install datum-mcp

# Upgrade datumctl
brew upgrade datum-mcp

Always helpful to have a simple upgrade path through a package manager especially when there's version changes.