Enable third party contributions

- Add instructions for contributing to ARM Trusted Firmware.

- Update copyright text in all files to acknowledge contributors.

Change-Id: I9311aac81b00c6c167d2f8c889aea403b84450e5
diff --git a/arch/system/gic/aarch64/gic_v3_sysregs.S b/arch/system/gic/aarch64/gic_v3_sysregs.S
index ecbc1f7..cb5dd79 100644
--- a/arch/system/gic/aarch64/gic_v3_sysregs.S
+++ b/arch/system/gic/aarch64/gic_v3_sysregs.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, ARM Limited. All rights reserved.
+ * Copyright (c) 2013, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
diff --git a/arch/system/gic/gic.h b/arch/system/gic/gic.h
index f38f42b..e4beb56 100644
--- a/arch/system/gic/gic.h
+++ b/arch/system/gic/gic.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, ARM Limited. All rights reserved.
+ * Copyright (c) 2013, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
diff --git a/arch/system/gic/gic_v2.c b/arch/system/gic/gic_v2.c
index f8de290..6c928d5 100644
--- a/arch/system/gic/gic_v2.c
+++ b/arch/system/gic/gic_v2.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, ARM Limited. All rights reserved.
+ * Copyright (c) 2013, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
diff --git a/arch/system/gic/gic_v2.h b/arch/system/gic/gic_v2.h
index c944df6..284c874 100644
--- a/arch/system/gic/gic_v2.h
+++ b/arch/system/gic/gic_v2.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, ARM Limited. All rights reserved.
+ * Copyright (c) 2013, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
diff --git a/arch/system/gic/gic_v3.h b/arch/system/gic/gic_v3.h
index a4fe2ce..9777cf9 100644
--- a/arch/system/gic/gic_v3.h
+++ b/arch/system/gic/gic_v3.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, ARM Limited. All rights reserved.
+ * Copyright (c) 2013, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met: