Add list of algorithms and functions supported to readme

[rmhrisk]

It would be useful to have an examples frontpage on
node-webcrypto-ossl's REAMDE.md github frontpage, much like
https://github.com/diafygi/webcrypto-examples has. That way developers
can quickly see what functions are implemented, and how they should
use them.

[rmhrisk]

This is another way to represent this information https://www.chromium.org/blink/webcrypto

[microshine]

@rmhrisk
https://github.com/PeculiarVentures/node-webcrypto-ossl#supported-algorithms

SHould it be closed?