doc: more explicit crypto.pseudoRandomBytes docs

Updates the docs for the crypto.pseudoRandomBytes function
to more explicitly detail how it's the same as crypto.randomBytes
just without a safety net (e.g. it doesn't throw an error when
there is low entropy).

PR-URL: #545
Reviewed-By: Ben Noordhuis <[email protected]>

Author: calvinmetcalf

doc/api/crypto.markdown

@@ -654,13 +654,9 @@ are drained.
 
 ## crypto.pseudoRandomBytes(size[, callback])
 
-Generates *non*-cryptographically strong pseudo-random data. The data
-returned will be unique if it is sufficiently long, but is not
-necessarily unpredictable. For this reason, the output of this
-function should never be used where unpredictability is important,
-such as in the generation of encryption keys.
-
-Usage is otherwise identical to `crypto.randomBytes`.
+Identical to `crypto.randomBytes` except that, instead of throwing an error when
+there is not enough accumulated entropy to generate cryptographically strong
+data, it will silently return **non**-cryptographically strong data.
 
 ## Class: Certificate