README: Add details for PLDM for File Transfer client function

Signed-off-by: Jeremy Kerr <[email protected]>

Author: jk-ozlabs

README.md

@@ -35,6 +35,24 @@ To incorporate NVMe-MI responder support, add the `nvme-mi` feature:
 cargo build --features nvme-mi
 ```
 
+We also support a test client for PLDM for File Transfer (type 7). When
+`mctp-dev` is assigned an MCTP EID, it will perform PLDM operations to
+read a file from the bus owner EID.
+
+The PLDM client expects to find the File record as the first PDR entry, and
+will attempt to transfer the entire file. Upon completion, the file size and
+sha256 checksum will be printed:
+
+```
+11:06:34 [INFO] Transfer complete. 16384 bytes, sha256 b4d3f1859dc8170c1e1f34b936aff05339a7723b6680894380c23dd84ff7e22b
+```
+
+To enable the PLDM File functionality, add the `pldm` feature:
+
+```sh
+cargo build --features pldm
+```
+
 # Running
 
 1. Run `qemu` with a usbredir connection to a pty: