add docstring, update changelog

CHANGELOG.md

@@ -5,6 +5,11 @@
 ### Data and metadata rework
 
 * Outputs check compatibility between metadata of inputs if there is more than one target input (!104)
+* Add data tools function `check_units(lhs, rhs)` to check for convertibility (!105)
+
+### Components
+
+* Add `merger.WeightedSum` for aggregation of multiple inputs
 
 ## [v0.4.0-rc.2]
 

src/finam/modules/mergers.py

@@ -6,7 +6,17 @@ from ..tools.log_helper import LogError
 
 
 class WeightedSum(AComponent):
-    """Merges inputs by weighted sum"""
+    """Merges inputs by weighted sum
+
+    Parameters
+    ----------
+    inputs : list(str)
+        Base input names; will create two inputs for each entry: "<name>" and "<name>_weight"
+    start : datetime.datetime
+        Starting time, for initial data exchange
+    grid : GridBase or None
+        Expected input grid specification; tries to obtain grid specs from inputs if set to None
+    """
 
     def __init__(self, inputs, start, grid=None):
         super().__init__()