Add note to api about pace plans in active dev
Add note to api about pace plans in active dev

I tried to use @note and it wasn't working and probably not
what we want anyway if it applied to the top-level instead of
this one argument.

closes LS-2615
flag=none

test plan:
- generate api docs: rake doc:api
- view Update a Course docs
  /doc/api/courses.html#method.courses.update
- Should see a note for enable_pace_plans being in active
  development

Change-Id: I9d3bacaa99110037ba749ffb0521aaac478f48a2
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/273675
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Jackson Howe <318c10a818c1b1f2ec50cdcb1827b2c6c5ebd7dc@instructure.com>
QA-Review: Jackson Howe <318c10a818c1b1f2ec50cdcb1827b2c6c5ebd7dc@instructure.com>
Product-Review: Nate Armstrong <619b324efbf5f7848de055bdc8bef4c0dd7c8ef5@instructure.com>

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