doc: clarify protobuf build requirements

Author: fanquake

doc/build-unix.md

@@ -44,7 +44,7 @@ Optional dependencies:
  miniupnpc   | UPnP Support     | Firewall-jumping support
  libdb4.8    | Berkeley DB      | Wallet storage (only needed when wallet enabled)
  qt          | GUI              | GUI toolkit (only needed when GUI enabled)
- protobuf    | Payments in GUI  | Data interchange format used for payment protocol (only needed when GUI enabled)
+ protobuf    | Payments in GUI  | Data interchange format used for payment protocol (only needed when BIP70 enabled)
  libqrencode | QR codes in GUI  | Optional for generating QR codes (only needed when GUI enabled)
  univalue    | Utility          | JSON parsing and encoding (bundled version will be used unless --with-system-univalue passed to configure)
  libzmq3     | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.0.0)

doc/dependencies.md

@@ -35,7 +35,7 @@ Some dependencies are not needed in all configurations. The following are some f
 #### Options passed to `./configure`
 * MiniUPnPc is not needed with  `--with-miniupnpc=no`.
 * Berkeley DB is not needed with `--disable-wallet`.
-* protobuf is not needed with `--disable-bip70`.
+* protobuf is only needed with `--enable-bip70`.
 * Qt is not needed with `--without-gui`.
 * If the qrencode dependency is absent, QR support won't be added. To force an error when that happens, pass `--with-qrencode`.
 * ZeroMQ is needed only with the `--with-zmq` option.