docs: Add NumPy ndarray .argmax() method documentation (#7911)

* docs: Add NumPy ndarray .argmax() method documentation

Created comprehensive NumPy ndarray .argmax() method documentation including:

- Complete front matter with Data Science subjects and tags
- Clear definition and syntax
- Detailed parameters (axis, out) and return values
- Three practical code examples with outputs
- Codebyte interactive example with student scores

Fixes #7859
Submitted for Hacktoberfest 2025.

* Update argmax.md

---------

Author: Priyanshjain10

content/numpy/concepts/ndarray/terms/argmax/argmax.md

@@ -0,0 +1,137 @@
+---
+Title: '.argmax()'
+Description: 'Returns the indices of the maximum values along a specified axis.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Arrays'
+  - 'Methods'
+  - 'NumPy'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/data-science'
+---
+
+The **`.argmax()`** method returns the indices of the maximum values along a specified axis in a NumPy ndarray.
+
+## Syntax
+
+```pseudo
+ndarray.argmax(axis=None, out=None, *, keepdims=False)
+```
+
+**Parameters:**
+
+- `axis` (int, optional): Axis along which to find the maximum value; flattens the array if `None`.
+- `out` (ndarray, optional): Output array to store the result; must match the expected shape.
+- `keepdims` (bool, optional): If `True`, retains reduced dimensions with size 1.
+
+**Return value:**
+
+Returns an integer or ndarray of integers indicating the indices of the maximum values.
+
+## Example 1: Finding Maximum Index in 1D Array
+
+In this example, the `.argmax()` method returns the index of the maximum value in a one-dimensional array:
+
+```py
+import numpy as np
+
+arr = np.array([3, 1, 4, 1, 5, 9, 2])
+max_index = arr.argmax()
+
+print("Array:", arr)
+print("Index of maximum value:", max_index)
+print("Maximum value:", arr[max_index])
+```
+
+The output of this code is:
+
+```shell
+Array: [3 1 4 1 5 9 2]
+Index of maximum value: 5
+Maximum value: 9
+```
+
+## Example 2: Finding Maximum Indices Along Axis in 2D Array
+
+In this example, the `.argmax()` method finds the indices of maximum values along each axis in a two-dimensional array:
+
+```py
+import numpy as np
+
+matrix = np.array([[1, 5, 3],
+                   [9, 2, 8],
+                   [4, 7, 6]])
+
+# Maximum index along axis 0 (columns)
+max_col = matrix.argmax(axis=0)
+
+# Maximum index along axis 1 (rows)
+max_row = matrix.argmax(axis=1)
+
+print("Matrix:")
+print(matrix)
+print("\nMax indices along axis 0 (columns):", max_col)
+print("Max indices along axis 1 (rows):", max_row)
+```
+
+The output of this code is:
+
+```shell
+Matrix:
+[[1 5 3]
+ [9 2 8]
+ [4 7 6]]
+
+Max indices along axis 0 (columns): [1 2 1]
+Max indices along axis 1 (rows): [1 0 1]
+```
+
+## Example 3: Flattened Array Maximum
+
+In this example, the `.argmax()` method returns the index of the maximum element from the flattened version of the array:
+
+```py
+import numpy as np
+
+matrix = np.array([[10, 25, 15],
+                   [30, 20, 35]])
+
+# Find index in flattened array
+flat_max_index = matrix.argmax()
+
+print("Matrix:", matrix)
+print("Index of maximum in flattened array:", flat_max_index)
+print("Maximum value:", matrix.flat[flat_max_index])
+```
+
+The output of this code is:
+
+```shell
+Matrix: [[10 25 15]
+ [30 20 35]]
+Index of maximum in flattened array: 5
+Maximum value: 35
+```
+
+## Codebyte Example
+
+In this example, the `.argmax()` method identifies the student with the highest score using their index position:
+
+```codebyte/python
+import numpy as np
+
+# Create sample data
+scores = np.array([85, 92, 78, 95, 88])
+students = ['Alice', 'Bob', 'Carol', 'David', 'Eve']
+
+# Find the student with highest score
+top_student_index = scores.argmax()
+
+print(f"Scores: {scores}")
+print(f"Highest score index: {top_student_index}")
+print(f"Top student: {students[top_student_index]}")
+print(f"Score: {scores[top_student_index]}")
+```