feat: add the docs

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Author: anandkaranubc

lib/node_modules/@stdlib/stats/incr/wstdev/docs/img/equation_weighted_standard_deviation.svg

@@ -0,0 +1,44 @@
+
+{{alias}}( [mean] )
+    Returns an accumulator function which incrementally computes a weighted
+    standard deviation.
+
+    If provided arguments, the accumulator function returns an updated weighted
+    standard deviation. If not provided arguments, the accumulator function
+    returns the current weighted standard deviation.
+
+    If provided `NaN` or a value which, when used in computations, results in
+    `NaN`, the accumulated value is `NaN` for all future invocations.
+
+    The accumulator function accepts two arguments:
+
+    - x: value.
+    - w: weight.
+
+    Parameters
+    ----------
+    mean: number (optional)
+        Known mean.
+
+    Returns
+    -------
+    acc: Function
+        Accumulator function.
+
+    Examples
+    --------
+    > var accumulator = {{alias}}();
+    > var mu = accumulator()
+    null
+    > mu = accumulator( 2.0, 1.0 )
+    0.0
+    > mu = accumulator( 3.0, 2.0 )
+    ~0.471
+    > mu = accumulator( 2.0, 0.1 )
+    ~0.478
+    > mu = accumulator()
+    ~0.478
+
+    See Also
+    --------
+