BIP-0158: clarify OP_RETURN handling for filters

In this commit, we clarify how we handle `OP_RETURN` outputs for regular
filters. The prior language was a bit ambiguous, so we hope to make it
as explicit as possible.

Author: Roasbeef

bip-0158.mediawiki

@@ -281,10 +281,10 @@ following items for each transaction in a block:
 
 Any "nil" items MUST NOT be included into the final set of filter elements.
 
-We exclude all <code>OP_RETURN</code> outputs in order to allow filters to
-easily be committed to in the future via a soft-fork. A likely area for future
-commitments is an additional <code>OP_RETURN</code> output in the coinbase
-transaction similar to the current witness commitment
+We exclude all outputs taht start with <code>OP_RETURN</code> in order to allow
+filters to easily be committed to in the future via a soft-fork. A likely area
+for future commitments is an additional <code>OP_RETURN</code> output in the
+coinbase transaction similar to the current witness commitment
 <ref>https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki</rev>. By
 excluding all <code>OP_RETURN</code> outputs we avoid a circular dependency
 between the commitment, and the item being committed to.