Add docstring for cirq.QasmOutput (#3934)

Adds docstring for `cirq.QasmOutput` and fixes formatting.

Fixes #3658.

cirq/circuits/circuit.py

@@ -2004,8 +2004,8 @@ def insert_at_frontier(
         """Inserts operations inline at frontier.
 
         Args:
-            operations: the operations to insert
-            start: the moment at which to start inserting the operations
+            operations: The operations to insert.
+            start: The moment at which to start inserting the operations.
             frontier: frontier[q] is the earliest moment in which an operation
                 acting on qubit q can be placed.
         """

cirq/circuits/qasm_output.py

@@ -167,6 +167,18 @@ def __init__(
         precision: int = 10,
         version: str = '2.0',
     ) -> None:
+        """Representation of a circuit in QASM format.
+
+        Args:
+            operations: Tree of operations to insert.
+            qubits: The qubits used in the operations.
+            header: A multi-line string that is placed in a comment at the top
+                of the QASM.
+            precision: The number of digits after the decimal to show for
+                numbers in the QASM code.
+            version: The QASM version to target. Objects may return different
+                QASM depending on version.
+        """
         self.operations = tuple(ops.flatten_to_ops(operations))
         self.qubits = qubits
         self.header = header