Convert Minimum Accounts Memo to Markdown

[allejo]

This PR converts the PDF to markdown but also touches the CSS to add support for footnotes and set a precedent on how to handle images with captions.

Closes #311

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[thekaveman]

This is great work on the footnotes especially!

One tiny change requested to get the pill filtering to work.

And one question for Marissa.

[mrose914]

Looks great! One add'l change is to see if we can make the font size of the footnotes a size or two smaller than the rest of the text on the page and/or potentially add a bit more space above just to clearly distinguish it from the body of the content. Below is a footnote example from MobiMart with the smaller font. Thank you!

[allejo]

I'm not concerned about this from an accessibility perspective because the <div> that Kramdown generates has a role="doc-endnotes".

[thekaveman]

Very nice 👍

[mrose914]

LGTM, thank you!

[machikoyasuda]

@allejo Hey Vlad - I'm trying to match the footnote style set here in #364 and #354 - but I can't figure out how you get the doc-backlink to show up. What is this sorcery?

Also, question, is having a heading called Footnotes a best practice/requirement?

[allejo]

@machikoyasuda okay, so there's some stuff to take note of for footnotes.

1. I am using Kramdown syntax for footnotes; this is not a CommonMark standard

   ...about 1 in 4 people in California are unbanked[^1] or underbanked[^2]...
   
   [^1]: Unbanked refers to people who have no access to a checking or savings account with an FDIC insured institution.
   [^2]: Underbanked refers to people who have a checking or savings account but regularly rely on alternative financial services such as money orders or payday loans.

   Source: https://github.com/cal-itp/calitp.org/pull/322/files#diff-4abe0f39e690bd5a0e8e745532e5b06dadbe649f4a0750076546847e38aba8a5R11-R19

2. Kramdown will automatically generate the "footnotes" section for you once you've included at least one footnote. I added the Footnotes "heading" via CSS so that it's visually there (this is part of Jekyll's rendered markdown, so you can't edit anything in the middle easily), but it doesn't tell screen readers to treat it like a heading. Kramdown automatically adds the doc-noteref and doc-endnote roles to that footnotes list, which are roles specified in WAI-ARIA 1.0

   And I've got some CSS to make the UI/UX visually appealing, https://github.com/cal-itp/calitp.org/pull/322/files#diff-4e9ead19074dc06fa9b4dce5cbbb7b06d97725dc022be3f4263abf99a02ec64fR221-R257