extensions: more README

Change-Id: I9cd902ce606c800e67cc142daf698962544b26bc

extensions/README

-Browser plugin, activex control, scanner bits.  Online update.
+This module contains a grab-bag of unrelated misc. libraries, *none* of which is an extension.
 
 == Application online update checking ==
 
@@ -12,3 +12,34 @@ This creates one more thread, UpdateCheckThread, that regularly checks whether
 we have reached the time when we should ask for the update.  If yes, asks for
 that, and shows the download button in the menu (if the new update is
 available).
+
+== OLE automation bridge ==
+
+A bridge between "OLE automation" and UNO, so you can use UNO services
+from JScript, VBScript, etc.
+
+https://www.openoffice.org/udk/common/man/spec/ole_bridge.html
+
+See udkapi/com/sun/star/bridge/oleautomation/ApplicationRegistration.idl
+
+This is initialized in Desktop::Main() in Desktop::OpenClients_Impl()
+by creating the service "com.sun.star.bridge.OleApplicationRegistration",
+which is implemented by ole_adapter::OleServer_Impl.
+
+See extensions/source/ole/
+
+== ActiveX control ==
+
+This allows embedding LO into a Win32 application as an ActiveX control.
+See extensions/source/activex/
+
+== Spotlight provider ==
+
+On Mac OS X, this allows indexing ODF documents with Spotlight.
+See extensions/source/macosx/spotlight/
+
+== Scanner support ==
+
+You can scan from LibreOffice, using platform specific backends like TWAIN/SANE.
+See extensions/source/scanner/
+