Edit README.asn1

Add another blank line before section headers.  Avoid contractions.
Change some whiches to thats where it seems appropriate.  Fix some
missing or extra words.
Fix error message quotations in install_kdc.rst

Some error messages that kprop could print were quoted incorrectly in
install_kdc.rst.

Also fix minor typos.

ticket: 7785 (new)
target_version: 1.12
tags: pullup