Fix three review findings in help text, example config and terms

The snapshot restore help splits its 40-word permissions sentence in
two. The snapshot-ID case leaves the parenthesis, and the temporary
space requirement gets its own sentence.

configs/config.example.yml gains a commented-out env entry, after
hostname, so its first line, which says the file shows every option,
is true again.

docs/REPOSTRUCTURE.md defines remote key in Terms, before the
marker-file section uses it.

Model: fable-5-1

configs/config.example.yml

@@ -375,3 +375,9 @@ compression_level: 5
 # Hostname to use in backup metadata
 # Default: system hostname
 #hostname: myserver
+
+# Environment variables that vaultik sets in its own process when it loads
+# the config. Its keys are variable names
+# Default: none
+#env:
+#  NAME: value