RZESZOW, Poland (Reuters) – The first U.S. troops reinforcing NATO allies in Eastern Europe amid a Russian military build-up on Ukraine’s border arrived on Saturday at Rzeszow military base in southeastern Poland. A small plane carrying what a Polish military source said were U.S. chain of command personnel landed at Rzeszow-Jasionka airport as preparations continued at the base, which is near Poland’s border with Ukraine. TV footage showed temporary accommodation being prepared at the G2A Arena in the nearby town of Jasionka, while workers could be seen building a fence around the venue. “As …