News: Overhauls README.en.txt

• Changes headline style from 'Title Case' to 'down case' (sentence style) as it is more popular with online publications and non-US countries. (E.g. see https://www.thoughtco.com/ which-words-in-a-title-should-be-capitalized-1691026) ((^ the above URL has been broken to overcome some overaggressive line length limiting commit hook))
• Adds a hint that the english compendium is outdated.
• Adds 'system requirements' which is take from https://www.gpg4win.org/system-requirements.html and points there.
• Removes section Installation because it shrank and put remaining info in first section.
• Changes: Fixes (en) <-> (de) confusions
• Additional notes: Moves more important GpgOL hints to the top.
• Additional notes: Makes Outlook 2003/2007 section more consistent so readers can be sure that the recommendation for an extra backup is only related to these versions of outlook. (Apart from the general advise to keep backups of all important data, an additional warning for GpgOL for Outlook 2010 or later has is not adaquate as no exceptional risks are known.)
• Removes closing, because a greeting can better be done in an announcement. And our one was a bit cryptic (sic!) anyway.