docs: improve split-operator documentation

I've added a high level description which I think better classifies and summarises this approach to solving a problem.

I've used the term meta algorithm, because this can be applied to a wide number of problems, with different, contextual and situational concrete algorithms.

Author: Lewiscowles1986

contents/split-operator_method/split-operator_method.md

@@ -1,5 +1,9 @@
 # The Split-Operator Method
-The Split-Operator Method (also called the Split-Step Method), was actually the primary method I used to solve the Schrödinger equation during my PhD.
+The Split-Operator Method (also called the Split-Step Method) can be best understood, as a problem-solving approach or meta-algorithm rather than a standalone algorithm, which solves a single problem.
+
+It describes a way of decomposing complex problems into smaller, more manageable subproblems, which can then be solved iteratively or in parallel.
+
+This was the primary method I used to solve the Schrödinger equation during my PhD.
 It is one of the simplest and fastest methods for this purpose and is widely used throughout modern quantum research in the area, in particular when dealing with the Non-linear Schrödinger Equation (NLSE):
 
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