[gbinder] Updated README

README

@@ -1,7 +1,44 @@
 GLib-style interface to binder (Android IPC mechanism)
 
-Provides:
+Key features:
 
 1. Integration with GLib event loop
 2. Detection of 32 vs 64 bit kernel at runtime
 3. Asynchronous transactions that don't block the event thread
+4. Stable service manager and low-level transation APIs
+
+Android keeps changing both low-level RPC and service manager
+protocols from version to version. To counter that, libgbinder
+implements configirable backends for different variants of those,
+and yet keeping its own API unchanged.
+
+Configuration is loaded from [Protocol] and [ServiceManager] sections
+of /etc/gbinder.conf file. The keys are binder device names or the
+special Default value, the value is the identifier of the protocol
+or service manager variant, respectively.
+
+In addition to reading /etc/gbinder.conf if it exists, /etc/gbinder.d
+directory is scanned for .conf files, the file list is sorted, files are
+loaded one by one, overwriting the entries loaded from /etc/gbinder.conf
+or from the previously processed file.
+
+Known protocol and service manager variants are aidl, aidl2 and hidl.
+This list is expected to expand further in the future. The default
+configuration is as follows:
+
+  [Protocol]
+  Default = aidl
+  /dev/binder = aidl
+  /dev/hwbinder = hidl
+
+  [ServiceManager]
+  Default = aidl
+  /dev/binder = aidl
+  /dev/hwbinder = hidl
+
+Alternatively, one can specify the desired Android API level:
+
+  [General]
+  ApiLevel = 29
+
+and let libgbinder pick the appropriate preset.