Soong: Add synopsis to cc_library_* modules

Added synopsis to the following modules under cc package:
   * cc_library_static
   * cc_library_shared
   * cc_library
   * cc_library_host_static
   * cc_library_host_shared
   * cc_library_headers

Bug: b/128337482
Test: Generated the documentation and verified that the synopsis was
added to each of the module.

Change-Id: I4d9bb622dc75aad9ea1b9f331c80ed56ddbc9a15
diff --git a/cc/library.go b/cc/library.go
index e5bb347..bb2e1df 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -153,42 +153,48 @@
 	android.RegisterModuleType("cc_library_headers", LibraryHeaderFactory)
 }
 
-// Module factory for combined static + shared libraries, device by default but with possible host
-// support
+// cc_library creates both static and/or shared libraries for a device and/or
+// host. By default, a cc_library has a single variant that targets the device.
+// Specifying `host_supported: true` also creates a library that targets the
+// host.
 func LibraryFactory() android.Module {
 	module, _ := NewLibrary(android.HostAndDeviceSupported)
 	return module.Init()
 }
 
-// Module factory for static libraries
+// cc_library_static creates a static library for a device and/or host binary.
 func LibraryStaticFactory() android.Module {
 	module, library := NewLibrary(android.HostAndDeviceSupported)
 	library.BuildOnlyStatic()
 	return module.Init()
 }
 
-// Module factory for shared libraries
+// cc_library_shared creates a shared library for a device and/or host.
 func LibrarySharedFactory() android.Module {
 	module, library := NewLibrary(android.HostAndDeviceSupported)
 	library.BuildOnlyShared()
 	return module.Init()
 }
 
-// Module factory for host static libraries
+// cc_library_host_static creates a static library that is linkable to a host
+// binary.
 func LibraryHostStaticFactory() android.Module {
 	module, library := NewLibrary(android.HostSupported)
 	library.BuildOnlyStatic()
 	return module.Init()
 }
 
-// Module factory for host shared libraries
+// cc_library_host_shared creates a shared library that is usable on a host.
 func LibraryHostSharedFactory() android.Module {
 	module, library := NewLibrary(android.HostSupported)
 	library.BuildOnlyShared()
 	return module.Init()
 }
 
-// Module factory for header-only libraries
+// cc_library_headers contains a set of c/c++ headers which are imported by
+// other soong cc modules using the header_libs property. For best practices,
+// use export_include_dirs property or LOCAL_EXPORT_C_INCLUDE_DIRS for
+// Make.
 func LibraryHeaderFactory() android.Module {
 	module, library := NewLibrary(android.HostAndDeviceSupported)
 	library.HeaderOnly()