docs: add code sample and docstring for bpd.options.experiments.sql_compiler.

Added documentation for the sql_compiler property.

Author: tswast

bigframes/_config/experiment_options.py

@@ -72,6 +72,13 @@ def ai_operators(self, value: bool):
 
     @property
     def sql_compiler(self) -> Literal["legacy", "stable", "experimental"]:
+        """Set to 'experimental' to try out the latest in compilation experiments..
+
+        **Examples:**
+
+            >>> import bigframes.pandas as bpd
+            >>> bpd.options.experiments.sql_compiler = 'experimental'  # doctest: +SKIP
+        """
         return self._sql_compiler
 
     @sql_compiler.setter