"Usage" refers to `sh` instead of `bash`

[abbfefef]

Description certbot-route53.sh has bash-specific features, see #2.

Per documentation:

3. Download the certbot-route53.sh script.
+++
chmod a+x certbot-route53.sh
4. Run the script with your (comma-separated) domain(s) and email address:
sh certbot-route53.sh \
+++

Error sh certbot-route53.sh ... would fail if sh is not bash-compatible. (for example it's link to the minimalistic /bin/dash on Ubuntue 16.0.4 LTS)

Suggestion

1. [recommended] Remove sh in step 4 -- the script is made executable(chmod a+x ...) in step 3
2. Alternatively: replace sh with bash in step 4: bash certbot-route53.sh ...