[docs] Missing example

[hamza-shezad]

Reference: https://github.com/mergeability/mergeable/blob/590a40fa9ab9a5f3adbc11273687f043beb91aec/docs/validators/stale.rst?plain=1#L21

Not sure if "See a full example" is referring to the example above it. If not, please add the example to complete the documentation.