allow copy and paste from readme

spare people the time deleting $ from text.

src/README.md

@@ -40,20 +40,22 @@ You can also get the source by "git clone" our git repository. Make sure you
 have also cloned the submodules and generated the configure script (skip this
 if you are using a release .tar.gz or .zip package):
 
-    $ git clone https://github.com/protocolbuffers/protobuf.git
-    $ cd protobuf
-    $ git submodule update --init --recursive
-    $ ./autogen.sh
-
+```shell
+    git clone https://github.com/protocolbuffers/protobuf.git
+    cd protobuf
+    git submodule update --init --recursive
+    ./autogen.sh
+```
 To build and install the C++ Protocol Buffer runtime and the Protocol
 Buffer compiler (protoc) execute the following:
 
-    $ ./configure
-    $ make
-    $ make check
-    $ sudo make install
-    $ sudo ldconfig # refresh shared library cache.
-
+```shell
+     ./configure
+     make
+     make check
+     sudo make install
+     sudo ldconfig # refresh shared library cache.
+```
 If "make check" fails, you can still install, but it is likely that
 some features of this library will not work correctly on your system.
 Proceed at your own risk.
@@ -83,10 +85,12 @@ Protocol Buffers integrates with pkg-config to manage this.  If you
 have pkg-config installed, then you can invoke it to get a list of
 flags like so:
 
+
     pkg-config --cflags protobuf         # print compiler flags
     pkg-config --libs protobuf           # print linker flags
     pkg-config --cflags --libs protobuf  # print both
 
+
 For example:
 
     c++ my_program.cc my_proto.pb.cc `pkg-config --cflags --libs protobuf`
@@ -97,6 +101,7 @@ not pass the correct set of flags to correctly link against
 libprotobuf.  If the package in question uses autoconf, you can
 often fix the problem by invoking its configure script like:
 
+
     configure CXXFLAGS="$(pkg-config --cflags protobuf)" \
               LIBS="$(pkg-config --libs protobuf)"
 
@@ -118,15 +123,15 @@ of "protobuf" in these examples.
 For a Mac system, Unix tools are not available by default. You will first need
 to install Xcode from the Mac AppStore and then run the following command from
 a terminal:
-
-    $ sudo xcode-select --install
-
+```shell
+    sudo xcode-select --install
+```shell
 To install Unix tools, you can install "port" following the instructions at
 https://www.macports.org . This will reside in /opt/local/bin/port for most
 Mac installations.
-
-    $ sudo /opt/local/bin/port install autoconf automake libtool
-
+```shell
+    sudo /opt/local/bin/port install autoconf automake libtool
+```
 Then follow the Unix instructions above.
 
 **Note for cross-compiling**