DOC: add tips how to deal with renaming conflicts

how-to-merge-after-rename.txt

+git merge linkahead-rename-step-1
+# resolve potential conflicts and commit
+rm -rf src/linkahead
+git mv src/caosdb/ src/linkahead
+rm -rf src/caosdb
+python3 create_slim_linkahead_wrapper.py
+git add src
+git ci -m "MAINT: rename caosdb to linkahead (module)"
+git merge linkahead-rename-step-2
+# resolve potential conflicts and commit
+git merge dev