[meta-tpm] README.md for meta-tpm layer seems incomplete

  here:

https://git.yoctoproject.org/meta-security/tree/meta-tpm/README.md

one reads:


The bbappend files for some recipes (e.g. linux-yocto) in this layer need
to have 'tpm' in DISTRO_FEATURES to have effect.
To enable them, add in configuration file the following line.

  DISTRO_FEATURES:append = " tpm"


but that does not mention the alternative of "tpm2" in
DISTRO_FEATURES, which is explicitly checked here:

https://git.yoctoproject.org/meta-security/tree/meta-tpm/classes/sanity-meta-tpm.bbclass

i will let one of the security people decide if they want to adjust
that.

rday