update docs (#253)

docs/README.md

@@ -1,6 +1,6 @@
 **SMAPI** is an open-source modding API for [Stardew Valley](http://stardewvalley.net/) that lets
 you play the game with mods. It's safely installed alongside the game's executable, and doesn't
-change any of your game files. It serves six main purposes:
+change any of your game files. It serves eight main purposes:
 
 1. **Load mods into the game.**  
    _SMAPI loads mods when the game is starting up so they can interact with it. (Code mods aren't
@@ -29,6 +29,14 @@ change any of your game files. It serves six main purposes:
    _SMAPI automatically checks for new versions of your installed mods, and notifies you when any
    are available._
 
+7. **Provide compatibility checks.**  
+   _SMAPI automatically detects outdated or broken code in mods, and safely disables them before
+   they cause problems._
+
+8. **Back up your save files.**  
+   _SMAPI automatically creates a daily backup of your saves and keeps ten backups, in case
+   something goes wrong. (Via the bundled SaveBackup mod.)_
+
 ## Documentation
 Have questions? Come [chat on Discord](https://discord.gg/KCJHWhX) with SMAPI developers and other
 modders!

docs/release-notes.md

@@ -2,6 +2,7 @@
 ## 2.6 beta
 * For players:
   * Updated for Stardew Valley 1.3 (no longer compatible with earlier versions).
+  * Added a bundled save backup mod.
   * Added beta update channel.
   * Added prompt when in beta channel and a new version is found.
   * Added friendly error when game can't start audio.