added mamba as recommended route

[shimwell]

Proposed changes

Adding details of how to use mamba for the install

Types of changes

What types of changes does your code introduce to the Paramak?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests