Merge pull request #549 from ipfs/docs/clarify-ed25519

docs: clarify unsupported ed25519

Author: achingbrain

SPEC/KEY.md

@@ -20,7 +20,7 @@ Where:
 
 - `name` is a local name for the key
 - `options` is an object that contains following properties
-  - 'type' - the key type, one of 'rsa'
+  - 'type' - the key type, one of 'rsa', 'ed25519' (Note: `js-ipfs` will not support 'ed25519' until [libp2p/js-libp2p-crypto#145](https://github.com/libp2p/js-libp2p-crypto/issues/145) is resolved)
   - 'size' - the key size in bits
 
 **Returns**