README.md: Update co-maintainer for meta-xilinx
README.md: Update co-maintainer for meta-xilinx

Update Manju as co-maintainer for meta-xilinx layer.

Signed-off-by: Manjukumar Matha <4c64a17569570cb9f1048973bce031c402b55312@xilinx.com>
Signed-off-by: Nathan Rossi <2e8aa918660411855c6d44d5bb2da677aa033255@nathanrossi.com>

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