docs: add more datetime examples (jrnl-org#1913)

note: commited file was generated from parsedatetime project (https://github.com/bear/parsedatetime)
with command
```
git grep --only-matching --heading -P "(?<=cal.parse\(')[^']*(?=')" -- :tests/* :^*Australian* :^*Errors* :^*German* :^*Locale* :^*Russian* | grep -v -P '.*\.py|\$300|300ml|25:23|14/32/2015|anhour|an hamburger'
```