Write a Python function `find_first_adverb` that takes a string as input and identifies the first adverb ending with "ly" in the string. The function should return a tuple containing the adverb and its start and end positions in the string. If no such adverb is found, return `None`.
#### Example Usage
```python [main.nopy]
find_first_adverb("Clearly, he has no excuse for such behavior.")
# Output: ('Clearly', 0, 7)
find_first_adverb("Please handle the situation carefully.")
# Output: ('carefully', 28, 37)
find_first_adverb("This sentence has no adverbs.")
# Output: None
```