docs: Add a new Config_Changes.md document

Add a document to track non-backwards compatible changes to the
printer config file.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Config_Changes.md

@@ -0,0 +1,9 @@
+This document covers recent software changes to the config file that
+are not backwards compatible. It is a good idea to review this
+document when upgrading the Klipper software.
+
+All dates in this document are approximate.
+
+# Changes
+
+20181220: Klipper v0.7.0 released

docs/FAQ.md

@@ -424,3 +424,7 @@ follow the full upgrade steps outlined above. Note that the RESTART
 and FIRMWARE_RESTART g-code commands do not load new software - the
 above "sudo service klipper restart" and "make flash" commands are
 needed for a software change to take effect.
+
+When upgrading the software, be sure to check the
+[config changes](Config_Changes.md) document for information on
+software changes that may require updates to your printer.cfg file.

docs/Overview.md

@@ -25,8 +25,11 @@ some common questions. The [G-Codes](G-Codes.md) document lists
 currently supported run-time commands.
 
 The history of Klipper releases is available at
-[releases](Releases.md). See [contact](Contact.md) for information on
+[releases](Releases.md). The [config changes](Config_Changes.md)
-bug reporting and general communication with the developers.
+document describes recent software changes that may require users to
+update their printer config file. See [contact](Contact.md) for
+information on bug reporting and general communication with the
+developers.
 
 Developer Documentation
 =======================