Updates via git pull destroy the work on HTML frontend. Maybe it is an idea to set www/src on .gitignore list or give a short text, how to set it on the exclude list.
For other readers, this seems to be a request about GitHub - deltachat/chatmail: chatmail service deployment scripts and docs repo.
Adding www/src to .gitignore will not solve the problem of merge conflicts if you modify the files already commited there. If you want to modify files there, create a local branch, change files and commit changes. Then when you update the repo, resolve merged conflicts manually and integrate or remove changes done to the upstream repo.