add a script to update core-rust

tools/update-core.sh

@@ -0,0 +1,22 @@
+
+# this script updates the deltachat-core-rust sub-repository from github.
+# must be executed from the repo root.
+#
+# - make sure, the deltachat-ios directory is clean
+# - make sure, deltachat-core-rust is committed successfully before calling this script
+
+# check out submodules as present in the repository
+git submodule update --init --recursive
+
+# update submodule
+cd deltachat-ios/libraries/deltachat-core-rust
+git checkout master
+git pull
+cd ../../..
+
+# commit changes
+git add deltachat-ios/libraries/deltachat-core-rust
+git commit -m "update deltachat-core-rust submodule"
+
+echo "changes are commited to local repo."
+echo "use 'git push' to use them or 'git reset HEAD~1; git submodule update --recursive' to abort on your own risk :)"