Suggestion: tweak text for proj:transform to warn off common pitfalls

[Kirill888]

projection/README.md

Lines 101 to 109 in 7f1d1c9

	#### proj:transform
	Linear mapping from pixel coordinate space (Pixel, Line) to projection coordinate space (Xp, Yp). It is
	a `3x3` matrix stored as a flat array of 9 elements in row major order. Since the last row is always `0,0,1` it can be omitted,
	in which case only 6 elements are recorded. This mapping can be obtained from
	GDAL([`GetGeoTransform`](https://gdal.org/api/gdaldataset_cpp.html#_CPPv4N11GDALDataset15GetGeoTransformEPd)) or the Rasterio
	([`Transform`](https://rasterio.readthedocs.io/en/stable/api/rasterio.io.html#rasterio.io.BufferedDatasetWriter.transform)).
	To get it on the command line you can use the [Rasterio CLI](https://rasterio.readthedocs.io/en/latest/cli.html) with the
	[info](https://rasterio.readthedocs.io/en/latest/cli.html#info) command: `$ rio info`.

Description above mentions GetGeoTransform and rio info. These two produce different formats on output, and while this extension is compatible with rio info, data from GetGeoTransform needs to be re-arranged. I think it's easy enough to assume that you can just stick output of GetGeoTransform into the stac document, but this is not the case.

[hobu]

Make a PR that updates the language and it is quite likely to be merged.