Add alt-text tags to Embed Boarding List Chart page

[o-fish-wildaid]

Add alt-text tags to the Embed Boarding List Chart page.

Page exists at: https://wildaid.github.io/charts/2020/06/12/Embed-Boardings-List.html In the code at: _posts/build_charts/2020-06-12-Embed-Boardings-List.md

A brief guide to alt-text tags can be found in our style guide at https://wildaid.github.io/style/2020/10/02/Alt-Text.html

[RuchaYagnik]

Hi @o-fish-wildaid, I have gone through the issue requisite and would like to contribute to it. I request to assign this issue to me, Thank you.

[Sheeri]

Hello! Thanks for expressing interest in this issue. Since you have been assigned issue #67 and haven't submitted a PR for it yet, we ask that you finish that issue first, before we assign another issue to you.

[GabbyJ]

Hi @Sheeri, I would like to work on this issue. Can you assign it to me?

[Sheeri]

Hello, thanks for offering to work on this! I have assigned it to you.