Say why the folders cannot be made instead of dying

Something already sitting where Documents/N1MM Logger+ should go — a file, or
a link to somewhere that is not there — threw out of Directory.CreateDirectory
before the program had a window, so the operator got a stack trace and nothing
else.

CreateFolders answers with what stopped it, and the program shows it in a
window naming the path and stops there. NONEMM_HOME moves the whole lot
somewhere else, for a station that keeps its files off the Documents folder.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

README.md

@@ -423,7 +423,13 @@ the migrations for N1MM's own admin databases and the program it speaks with,
 and neither has anything to do with a log.
 
 On a system that does not say where Documents is — most Linux systems, until
-someone sets `XDG_DOCUMENTS_DIR` — it is `~/Documents/N1MM Logger+`.
+someone sets `XDG_DOCUMENTS_DIR` — it is `~/Documents/N1MM Logger+`. Setting
+`NONEMM_HOME` puts the whole lot somewhere else, which is what a station keeping
+its files off the Documents folder, or running two copies side by side, wants.
+
+If a folder cannot be made — something else is already sitting at that path, or
+the disk will not have it — the program says so in a window and stops, rather
+than dying with a stack trace before it has a window to say anything in.
 
 ### Operators