Update RSS feed to properly include images

Hi, this is a first-timers-only issue. This means we've worked to make it more legible to folks who either haven't contributed to our codebase before, or even folks who haven't contributed to open source before.

If that's you, we're interested in helping you take the first step and can answer questions and help you out as you do. Note that we're especially interested in contributions from people from groups underrepresented in free and open source software!

If you have contributed before, consider leaving this one for someone new, and looking through our general help wanted issues. Thanks!

The problem

What's supposed to happen: MapKnitter maps in the "clean" feed are supposed to be tweeted out at http://twitter.com/mapknitter

But the images are all broken!

Solution

This was recently completed on PublicLa.org in this issue:

https://github.com/publiclab/plots2/issues/1958

Let's reproduce those fixes here, noting especially the final version of the RSS feed, here:

https://github.com/sagarpreet-chadha/plots2/blob/b866d864eba05f0c9316cdac505493d8e60e75e9/app/views/notes/rss.rss.builder#L1-L25

The corresponding MapKnitter code is here:

https://github.com/publiclab/mapknitter/blob/8b475376ef8951909c949634bfb06a68ff69bcff/app/views/feeds/clean.builder#L1-L24

Note especially this line, which inserts the image correctly into the post:

https://github.com/sagarpreet-chadha/plots2/blob/b866d864eba05f0c9316cdac505493d8e60e75e9/app/views/notes/rss.rss.builder#L12

That's the most important line to add into the MapKnitter feed!

Steps to Fix

• claim this issue with a comment here, below, and ask any clarifying questions you need
• set up a repository locally following the README instructions, and make sure that all tests pass
• try to fix the issue following the steps above, but even before you're done, you can:
• commit your changes and start a pull request (see contributing to Public Lab software) but mark it as "in progress" if you have questions or if you haven't finished
• alert someone via the developers list (see below) to have your pull request merged. This may take a few extra steps depending on when you do it, but we'll help you out!

Please email the developers list (see https://publiclab.org/wiki/developers) or go to the chatroom if you have questions, and take a look at our first-timers landing page for more information!

(This is a follow-up to old issue here: https://github.com/publiclab/mapknitter/pull/241)