Are you sure that the .md document you are referencing is being published to ShinyApps.io with your application? The error is that the markdown file cannot be found on shinyapps.io. This has no bearing on whether the file exists locally on your computer. It needs to be uploaded in the application bundle when publishing.
Specifically, I expect that the following elements are worth focusing on:
2018-03-22T00:26:38.303115+00:00 shinyapps[304597]: cannot open file '../docs/take_action.md': No such file or directory
2018-03-22T00:26:38.303112+00:00 shinyapps[304597]: Warning in readLines(con) :
2018-03-22T00:26:38.303657+00:00 shinyapps[304597]: Warning: Error in readLines: cannot open the connection
2018-03-22T00:26:38.308633+00:00 shinyapps[304597]: Error : An error has occurred. Check your logs or contact the app author for clarification.
Usually, dependent files are published in "subdirectories" of the app folder along with the application. i.e. referencing "../docs/take_action.md" means that the markdown file is not in a subdirectory, since ../ moves up the parent folder. Try moving the .md to a subdirectory, changing the relative path to point to its new location, and publishing the .md file along with the application.
Some more information on troubleshooting deployments can be found here: