Error in porkchop docstrings

[jorgepiloto]

🐞 Problem

While working with poliastro.plotting.porkchop I noticed that the docstring
regarding the output values for the porkchop function is not updated. There
are two missing values: dv_launch and dv_arrival. Both should be included.

💡 Possible solutions

• Add corresponding function docstrings.

📋 Steps to solve the problem

• Add, commit, run tests and push your changes
• Submit a pull request and add this in comments - Addresses #<put issue number here>
• Ask for a review in comments section of pull request
• Celebrate your contribution to this project 🎉

[iamabhishek0]

@jorgepiloto I would like to fix it. Will make a PR soon.

[jorgepiloto]

Thank you @iamabhishek0! 🚀

[iamabhishek0]

@priyanshurohilla I was working on it :)

[jorgepiloto]

@iamabhishek0 There is no problem usually if two users working on the same issue. We do normally merge the first PR to success all reviews and code tests 🚀

[iamabhishek0]

@jorgepiloto Sure, will keep that in mind.

[astrojuanlu]

Closed in #893.