* Set default value of SMTPFrom to empty string
This parameter should contain proper e-mail address (to be provided by user during configuration).
* Update default values in example/config.yaml
Default values and related comments in example/config.yaml are aligned
with values defined in internal/config/defaults.go.
Small improvements to foramting of config.yaml file.
* Add default value for AdvancedThrottlingRetryAfter to internal/config/defaults.go
AdvancedThrottlingRetryAfter was introduced in 70739d3 (superseriousbusiness/gotosocial#1466).
* Update config.yaml snippets in documentation