docs/integration: clarify tar compression formats
docs/integration: clarify tar compression formats

Previously it was not clear that CONFIG_FEATURE_SEAMLESS_XZ was an
example for one tar compression format, no comprehensive suggestion.
Make that clear.

Signed-off-by: Bastian Krause <591dbcb2d48f405f0cb405f5aa6519451f40ad30@pengutronix.de>

rauc/rauc,rauc/rauc,ejoerns/rauc,jluebbe/rauc,jluebbe/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc