README: rm "Compile the protobuf description file" section

The generated file "paymentrequest_pb2.py" is already committed into the repository,
so users don't need to run this command.
Further, the command itself is preserved in "paymentrequest.py"
(it gets printed if we cannot find the generated file).

README.rst

@@ -82,11 +82,6 @@ Run install (this should install dependencies)::
     python3 -m pip install --user .
 
 
-Compile the protobuf description file::
-
-    sudo apt-get install protobuf-compiler
-    protoc --proto_path=electrum --python_out=electrum electrum/paymentrequest.proto
-
 Create translations (optional)::
 
     sudo apt-get install python-requests gettext

electrum/paymentrequest.py

@@ -36,6 +36,7 @@ import aiohttp
 try:
     from . import paymentrequest_pb2 as pb2
 except ImportError:
+    # sudo apt-get install protobuf-compiler
     sys.exit("Error: could not find paymentrequest_pb2.py. Create it with 'protoc --proto_path=electrum/ --python_out=electrum/ electrum/paymentrequest.proto'")
 
 from . import bitcoin, ecc, util, transaction, x509, rsakey