Using proxy with docker

[lepeli]

Adding how to use a proxy with docker

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Short Description:

I just added a section for using a proxy with docker

Fixes/Resolves/Closes (please use correct syntax):

• Change on installation documentation

[mention-bot]

@lepeli, thanks for your PR! By analyzing the history of the files in this pull request, we identified @nivong, @walkerlee and @supercourgette to be potential reviewers.

[pogarek]

👍

[pogarek]

merged #6010