Update docs to make 3 basic configs match (#2117)

README.md

@@ -38,6 +38,7 @@ Or run:
 git config --global core.pager delta
 git config --global interactive.diffFilter 'delta --color-only'
 git config --global delta.navigate true
+git config --global delta.dark true  # or `delta.light true`, or omit for auto-detection
 git config --global merge.conflictStyle zdiff3
 ```
 

manual/src/get-started.md

@@ -10,11 +10,8 @@
     diffFilter = delta --color-only
 
 [delta]
-    navigate = true    # use n and N to move between diff sections
-
-    # delta detects terminal colors automatically; set one of these to disable auto-detection
-    # dark = true
-    # light = true
+    navigate = true  # use n and N to move between diff sections
+    dark = true      # or `light = true`, or omit for auto-detection
 
 [merge]
     conflictStyle = zdiff3