Update README.md

[carnoxen]

Fix a pest example. ident rule is more evidently.

[tomtau]

Thank you for fixing the example!
I assume this tries to fix the following issue: #551 , is that correct ?

if the fix is done in that way, it'll prevent all identifiers to start with a digit, not only the first one... so perhaps that description:

(...) where the first identifier does not start with a digit:

should be updated to:

(...) where identifiers do not start with a digit:

[carnoxen]

Thank you for fixing the example! I assume this tries to fix the following issue: #551 , is that correct ?

Yes it is. And I fixed the above sentence.