Update start-translating-openedx.rst

[jesgreco]

Adding the images to the document, and adding some text to better explain the steps to translate different strings.

[openedx-webhooks]

Thanks for the pull request, @jesgreco! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

All technical communication about the code itself will be done via the GitHub pull request interface. As a reminder, our process documentation is here.

Please let us know once your PR is ready for our review and all tests are green.

[jesgreco]

Please, @feanil cancel this PR as I've already included the link for the images within the document in PR# 420

[openedx-webhooks]

@jesgreco Even though your pull request wasn’t merged, please take a moment to answer a two question survey so we can improve your experience in the future.