add update_submodules.sh which checks out specific version

README.md

@@ -183,11 +183,10 @@ For example, [monero-java](https://github.com/monero-ecosystem/monero-java) comp
 		2. Copy libsodium.a to ./external-libs/libsodium.<br>
        Mac: installed through homebrew at /usr/local/Cellar/libsodium/1.0.17/lib/libsodium.a
 	5. Set up monero-project/monero:
-		1. Initialize submodules: `git submodule update --init --recursive`
+		1. Update submodules: `./bin/update_submodules.sh`
 		2. `cd ./external/monero-core`
-		3. `git checkout master`
-		3. Modify CMakeLists.txt: `option(BUILD_GUI_DEPS "Build GUI dependencies." ON)`.
-		4. Build **twice** to create libwallet_merged.a in addition to other .a libraries: `make release-static -j8`.
+		3. Modify CMakeLists.txt: `option(BUILD_GUI_DEPS "Build GUI dependencies." ON)`
+		4. Run twice to create libwallet_merged.a in addition to other .a libraries: `make release-static -j8`
 2. Link to this library's source files in your application or build as a shared library in `./build/`: `./bin/build_libmonero_cpp.sh`
        
 These build steps aspire to be automated further.  [Any help is greatly appreciated](https://github.com/monero-ecosystem/monero-cpp/issues/1).

bin/update_submodules.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+# initialize submodules recursively
+git submodule update --init --recursive
+
+# update monero-cpp
+git checkout master
+git pull --ff-only origin master
+
+# update monero-core
+cd ./external/monero-core
+git checkout master
+git pull --ff-only origin master
+cd ../../