Merge pull request #296 from pryrt/docMapGlobalStyle

add the Global Styles Document Map style

Author: pryrt

content/docs/preferences.md

@@ -481,6 +481,7 @@ Some of these styles apply to the background only, some apply to the foreground
 * Active tab text [foreground only] ⇒ Selects the colour to be used for the filename displayed in the titlebar of the active tab.
 * Inactive tabs [background and foreground] ⇒ Selects the colour to be used for the filename displayed in the titlebars of all inactive tabs.
 * URL hovered [foreground only] ⇒ If [Preferences > MISC. > Clickable Link](#misc) is enabled, when your cursor is hovering over a URL, the URL's foreground colour will follow this setting.
+* Document map [background and foreground] ⇒ The foreground color will be semi-transparently overlayed over the miniature version of text that's currently visible in the editor; the background color will be semi-transparently overlayed over the miniature version of the text that isn't currently visible in the editor (this style is new to v8.1.5).
 
 ### Search result styles