DOC: create acknowledgements

[aburrell]

Description

Create an acknowledgements template for pysat Ecosystem packages.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

N/A

Test Configuration

• Operating system: OS X Big Sur
• Version number: Python 3.9
• Any details about your local setup that are relevant

Checklist:

• [N/A] Make sure you are merging into the develop (not main) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have linted the files updated in this pull request
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes
• Update zenodo.json file for new code contributors

If this is a release PR, replace the first item of the above checklist with the
release checklist on the pysat wiki:
https://github.com/pysat/pysat/wiki/Checklist-for-Release