[README.md] Added a bit of credits

README.md

@@ -46,6 +46,20 @@ Forum posts:
 - [https://serverfault.com/questions/599103/make-a-docker-application-write-to-stdout](https://serverfault.com/questions/599103/make-a-docker-application-write-to-stdout)
 - [https://stackoverflow.com/questions/71557316/docker-alpine-execute-command-as-another-user](https://stackoverflow.com/questions/71557316/docker-alpine-execute-command-as-another-user)
 
+I learnt much about shell scripts (as I never did any shell coding before) while developing the [docker-entrypoint.sh](docker-entrypoint.sh) script, and forum posts, websites, etc. helped me alot along my journey (below just an excerpt):
+
+- [Shell exit codes explained](https://tldp.org/LDP/abs/html/exitcodes.html)
+- [The "shell script" if-else statement](https://linuxize.com/post/bash-if-else-statement/)
+- [The "shell script" while loop](https://www.cyberciti.biz/faq/bash-while-loop/)
+- [Checking environment variables](https://ioflood.com/blog/bash-check-if-environment-variable-is-set/)
+- [Another check for the existence of env vars](https://stackoverflow.com/questions/2981878/checking-for-environment-variables)
+- [Check if a variable is a number](https://www.baeldung.com/linux/bash-variable-is-numeric)
+- [Check for the existence of a directory](https://stackoverflow.com/questions/59838/how-do-i-check-if-a-directory-exists-or-not-in-a-bash-shell-script)
+- [Check if current directory is a git repository](https://stackoverflow.com/questions/2180270/check-if-current-directory-is-a-git-repository)
+- [Differences between the different braces in the shell](https://unix.stackexchange.com/questions/306111/what-is-the-difference-between-the-bash-operators-vs-vs-vs)
+
+Also, [ShellCheck](https://www.shellcheck.net/) helped me while developing and "optimizing" (if a total beginner can do so ;) this project.
+
 
 ## License