Remove Canvas upload README; add script comments

pages/upload-page-to-canvas.sh

@@ -11,16 +11,18 @@
 # Images are linked to their specified location on GitHub (the `GITHUB`
 # variable) and should be referenced to as e.g. `![](images/<some-image.png>)`
 # in the markdown.
-#
+
 # Links to pages on Canvas can be given using the URL to the page, but replacing
 # the course ID with the string 'COURSE_ID', which will then automatically build
-# the correct link by using the $COURSE_ID variable defined below. You can also
-# just provide the link using the markdown format: `[link text](<page-name>)`.
+# the correct link by using the $COURSE_ID variable defined below. The COURSE_ID
+# needs to be updated between course rounds, which is done by editing the
+# `pages/.course_id` file. You can also just provide the link using the markdown
+# format: `[link text](<page-name>)`.
 
-# TODO: what is the difference between using an explicit URL with course ID
-# (HTML) versus just using the path to the file (markdown)? The "course link
-# validator" seems to say markdown-based links are invalid even though they link
-# to the correct page with the correct course ID.
+# This script is run automatically in a GitHub Actions workflow which you can
+# find at `.github/workflows/canvas-upload.yml`. There is only one page that it
+# will run on, and that is the main landing page used as an example above, while
+# the rest of the course materials lives on GitHub pages.
 
 # Input parameters
 MARKDOWN=$1