Document the regenerateDelay configuration option

This documents the option added in commit ec74f14b6a7cb2cae24c015e038426600fd8f2ca.

core/config.html.md

@@ -67,6 +67,14 @@ docpadConfig = {
 	# An array of special paths that when changes occur in, we regenerate our website
 	regeneratePaths: []  # default
 
+	# Regenerate Delay
+	# The time (in milliseconds) to wait after a source file has
+	# changed before using it to regenerate. Updating over the
+	# network (e.g. via FTP) can cause a page to be partially
+	# rendered as the page is regenerated *before* the source file
+	# has completed updating: in this case increase this value.
+	regenerateDelay: 100    # default
+
 	# Out Path
 	# Where should we put our generated website files?
 	# If it is a relative path, it will have the resolved `rootPath` prepended to it