prompt user to provide a sync schedule

[adamsclafani]

simple change to inform a user that they must provide a sync schedule as well.

based on a suggestion from @holta

[codecov-commenter]

Codecov Report

Merging #553 (017c803) into master (3bf8167) will increase coverage by 1.73%.
The diff coverage is 55.97%.

@@            Coverage Diff             @@
##           master     #553      +/-   ##
==========================================
+ Coverage   76.71%   78.44%   +1.73%     
==========================================
  Files          45       51       +6     
  Lines        2766     3327     +561     
==========================================
+ Hits         2122     2610     +488     
- Misses        644      717      +73     

Impacted Files	Coverage Δ
opwen_email_server/config.py	100.00% <ø> (ø)
opwen_email_client/webapp/views.py	40.75% <21.05%> (-0.84%)	⬇️
opwen_email_client/webapp/tasks.py	43.58% <23.07%> (-3.08%)	⬇️
opwen_email_client/util/network.py	30.00% <30.00%> (ø)
opwen_email_client/webapp/actions.py	34.34% <30.95%> (-0.92%)	⬇️
opwen_email_client/webapp/forms/email.py	34.94% <60.00%> (-0.38%)	⬇️
opwen_email_client/webapp/forms/register.py	60.71% <60.71%> (ø)
opwen_email_server/services/sendgrid.py	91.79% <63.63%> (-2.61%)	⬇️
opwen_email_server/mailers/wikipedia.py	97.77% <97.77%> (ø)
opwen_email_client/webapp/config.py	100.00% <100.00%> (ø)
... and 7 more

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