Mention spec compliance matrix in the PR template (#886)
Mention spec compliance matrix in the PR template (#886)

Signed-off-by: Andrew Hsu <27e23b0e7806961c892b06fb3a239a19e45892e4@gmail.com>

Co-authored-by: Yuri Shkuro <16e6d622505a30b44c05fb8b6dfd2d798f782d4d@users.noreply.github.com>
open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification