Mention endianness and alignment in section ArrayBuffers, binary arrays

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* Alignment: My browser (Firefox 87.0 on Linux x86_64) doesn't let me create an unaligned Uint16Array. I. e., `new Uint16Array(b, 1, 1)` on a 4-byte array buffer gives `RangeError: attempting to construct out-of-bounds TypedArray on ArrayBuffer`. In the standard that is [22.2.1.5](https://262.ecma-international.org/6.0/#sec-%typedarray%-buffer-byteoffset-length).13a.

* Endianness: Uint16Array is little-endian on my machine. I just learned that this is machine dependent ([https://stackoverflow.com/questions/7869752/javascript-typed-arrays-and-endianness](Stackoverflow)). In contrast, `dataView.getUint16()` is big-endian, unless the second argument is true.

Hope this helps.

Find the tutorial section titled “ArrayBuffers, binary arrays” and review the existing explanation around typed arrays and DataView. Add clear notes covering alignment restrictions and the endianness distinction described in the issue, including the relevant behavior for Uint16Array and dataView.getUint16(). Done when readers can understand both caveats from that section.

Written by the indexing model from the issue text.