Add 'LICENSE.md' to the METplotpy repo

[lisagoodrich]

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Describe the Task

Add 'LICENSE.md' to the MET repo to define clearly/consistently define the s/w license we use, as described here...
https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/adding-a-license-to-a-repository
It's currently defined as Apache-2.0 in our documentation (e.g. https://github.com/dtcenter/MET/blob/main_v11.0/docs/Users_Guide/index.rst), but it might be wise to make it more front and center in the repo.

Existing license info can be found here:
https://met.readthedocs.io/en/latest/Users_Guide/index.html

Here is a quick video on how to do this: https://drive.google.com/file/d/1_CjTkqQb4BwE80ObYcxnddWb75S9IEsg/view?usp=share_link

Time Estimate

Estimate the amount of work required here.
Issues should represent approximately 1/2 day of work.

Sub-Issues

Consider breaking the task down into sub-issues.

• Add a checkbox for each sub-issue here.

Relevant Deadlines

List relevant project deadlines here or state NONE.

Funding Source

Split evenly between 2702691 and 2792541.

Define the Metadata

None

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Projects and Milestone

• Select Repository and/or Organization level Project(s) or add alert: NEED PROJECT ASSIGNMENT label
• Select Milestone as the next official version or Future Versions

Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy

Task Checklist

See the METplus Workflow for details.

• Complete the issue definition above, including the Time Estimate and Funding Source.
• Fork this repository or create a branch of develop.
  Branch name: feature_<Issue Number>_<Description>
• Complete the development and test your changes.
• Add/update log messages for easier debugging.
• Add/update unit tests.
• Add/update documentation.
• Push local changes to GitHub.
• Submit a pull request to merge into develop.
  Pull request: feature <Issue Number> <Description>
• Define the pull request metadata, as permissions allow.
  Select: Reviewer(s) and Development issues
  Select: Repository level development cycle Project for the next official release
  Select: Milestone as the next official version
• Iterate until the reviewer(s) accept and merge your changes.
• Delete your fork or branch.
• Close this issue.