Update readme with date stuff

Author: nkanu17

README.md

@@ -155,6 +155,7 @@ The layered approach emerged from TDD — writing tests first revealed natural b
 - [x] Vector KNN search: `vector_distance(field, :param)`
 - [x] Hybrid search (filters + vector)
 - [x] Full-text search: `LIKE 'prefix%'` (prefix), `fulltext(field, 'terms')` function
+- [x] Date functions: `YEAR()`, `MONTH()`, `DAY()`, `DATE_FORMAT()`, etc. (see below)
 
 ## What's Not Implemented (Yet...)
 
@@ -229,6 +230,11 @@ SELECT name, DATE_FORMAT(created_at, '%Y-%m-%d') AS date FROM events
 
 **Note:** Redis's `monthofyear()` returns 0-11 (not 1-12), and `dayofweek()` returns 0 for Sunday.
 
+#### Limitations
+
+- `NOT YEAR(field) = 2024` is not supported (raises `ValueError`)
+- `DATE_FORMAT()` is only supported in SELECT, not in WHERE (raises `ValueError`)
+- Date functions with `OR` require careful handling
 
 ## Development