[improvement] USER_GUIDE.md : minor update in text

[concese]

Hello.

On the following page https://github.com/openeuropa/oe_translation/blob/2.x/USER_GUIDE.md
Where it reads:
NOTE: Until ePoetry either Accepts or Rejects the request, no other request can be made to ePoetry for this Node.
It should be one of the following, or similar:
NOTE: Until DGT either Accepts or Rejects the request (in ePoetry), no other request can be made to ePoetry for this Node.
NOTE: Until DGT either Accepts or Rejects the request, no other request can be made to ePoetry for this Node.

Thank you
Sergio Parreira
COMM Europa Management