Update README.md

Author: JamesH65

hardware/raspberrypi/revision-codes/README.md

@@ -74,6 +74,7 @@ uuuuuuuuFMMMCCCCPPPPTTTTTTTTRRRR
 |          |              | 9: Zero                    |
 |          |              | a: CM3                     |
 |          |              | c: Zero W                  |
+|          |              | d: 3B+                     |
 | RRRR     | Revision     | 0, 1, 2, etc.              |
 
 New-style revision codes in use:
@@ -94,3 +95,4 @@ New-style revision codes in use:
 | a22042 | 2B (with BCM2837) | 1.2      | 1 GB   | Embest       |
 | a22082 | 3B                | 1.2      | 1 GB   | Embest       |
 | a32082 | 3B                | 1.2      | 1 GB   | Sony Japan   |
+| a020d3 | 3B+               | 1.3      | 1 GB   | Sony UK      |