adding non elastic MT number

[shimwell]

While making use of the reaction dictionary I noticed it does not have the mt number 3 for the nonelastic reaction. Perhaps this is a redundant reaction but might still be useful to add to this otherwise very complete dictionary of reactions.

Fixes # (issue)

Checklist

• I have performed a self-review of my own code
• I have followed the style guidelines for Python source files (if applicable)