Clarify IMedianizer isn't necessarily USD based

In preparation for an ETHBTC feed.

solidity/contracts/external/IMedianizer.sol

@@ -5,12 +5,12 @@ pragma solidity 0.5.17;
 interface IMedianizer {
     /// @notice Get the current price.
     /// @dev May revert if caller not whitelisted.
-    /// @return Price (USD) with 18 decimal places.
+    /// @return Designated price with 18 decimal places.
     function read() external view returns (uint256);
 
     /// @notice Get the current price and check if the price feed is active
     /// @dev May revert if caller not whitelisted.
-    /// @return Price (USD) with 18 decimal places.
+    /// @return Designated price with 18 decimal places.
     /// @return true if price is > 0, else returns false
     function peek() external view returns (uint256, bool);
 }