Update 'release-init.sh' script to update git submodules prior to starting the release process (#7517)

* Update submodules and added help text for release-init script

* updated some comments

Author: Michael Wilkerson-Barker

tools/release-init.sh

@@ -5,12 +5,33 @@
 # Description of release procedure can be found at https://github.com/realm/realm-wiki/wiki/Releasing-Realm-Core
 #
 
-realm_version=$(echo "$1" | egrep '^[0-9]?[0-9].[0-9]+.[0-9]+(-.*)?$')
+VERSION_GREP='^[0-9]?[0-9].[0-9]+.[0-9]+(-.*)?$'
+
+function usage()
+{
+    echo "Usage: release-init.sh VERSION"
+    echo "  VERSION format regex: ${VERSION_GREP}"
+    echo "  Examples:"
+    echo "    10.123.1"
+    echo "    99.999999.999999"
+    echo "    4.5.0-CustDemo"
+    exit 1
+}
+
+if [[ -z "$1" ]]; then
+    usage
+fi
+
+# egrep has been replaced with 'grep -E'
+realm_version=$(echo "$1" | grep -E "${VERSION_GREP}")
 if [ -z "${realm_version}" ]; then
     echo Wrong version format: "$1"
-    exit 1
+    usage
 fi
 
+# make sure submodules are up to date
+git submodule update --init --recursive
+
 project_dir=$(git rev-parse --show-toplevel)
 
 git branch release/${realm_version}