update docs to include instruction on displaying version in UI

[d-linko]

The UI uses the ANMS_VERSION variable in the header display. In the build.sh this was set automatically by

export GITTAG=$(git describe --always --tags --dirty)
export ANMS_VERSION=${ANMS_VERSION:=${GITTAG}}

This is only cosmetic and wont effect any functionality but moving forward these instructions needs to be included in start up documentation.

[mfarina1]

According to David Edell, this should be both a bug and documentation ticket. There should be a suitable default value (ie: git hash) or omit the version entirely if not defined.