[UIMA-6293] Migrate UIMA Parent POM to GitHub

- Move tag to new location

git-svn-id: https://svn.apache.org/repos/asf/uima/build/parent-pom/tags/parent-pom-6@1883117 13f79535-47bb-0310-9956-ffa450edef68
tree: 1800ac477e8307d09c6fb83741251295109f76cc
  1. README.txt
  2. marker-file-identifying-parent-pom
  3. pom.xml