[doc] gbuild: Set memory explicitly (default is too low)

doc/release-process.md

@@ -112,16 +112,16 @@ The gbuild invocations below <b>DO NOT DO THIS</b> by default.
 ### Build and sign Bitcoin Core for Linux, Windows, and OS X:
 
     pushd ./gitian-builder
-    ./bin/gbuild --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-linux.yml
+    ./bin/gbuild --memory 3000 --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-linux.yml
     ./bin/gsign --signer $SIGNER --release ${VERSION}-linux --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-linux.yml
     mv build/out/bitcoin-*.tar.gz build/out/src/bitcoin-*.tar.gz ../
 
-    ./bin/gbuild --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-win.yml
+    ./bin/gbuild --memory 3000 --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-win.yml
     ./bin/gsign --signer $SIGNER --release ${VERSION}-win-unsigned --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-win.yml
     mv build/out/bitcoin-*-win-unsigned.tar.gz inputs/bitcoin-win-unsigned.tar.gz
     mv build/out/bitcoin-*.zip build/out/bitcoin-*.exe ../
 
-    ./bin/gbuild --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
+    ./bin/gbuild --memory 3000 --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
     ./bin/gsign --signer $SIGNER --release ${VERSION}-osx-unsigned --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
     mv build/out/bitcoin-*-osx-unsigned.tar.gz inputs/bitcoin-osx-unsigned.tar.gz
     mv build/out/bitcoin-*.tar.gz build/out/bitcoin-*.dmg ../