add new howto to switch user

docs/user-guide/switching_users.md

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+# Switching Users
+
+In Linux there are several ways to switch between users. Some common methods are:
+
+```bash
+# Using su command
+su username
+su - username
+# Using sudo to switch user
+sudo su username
+sudo su - username
+```
+
+- `su username`: Switches to the specified user without loading their environment.
+- `su - username`: Switches to the specified user and loads their environment.
+- `sudo su username`: Switches to the specified user with superuser privileges without loading their environment.
+- `sudo su - username`: Switches to the specified user with superuser privileges and loads their environment.
+
+Depending on which command you are using the behavior and environment settings may differ. Also some commands will not acquire a kerberos ticket for the new user and therefore certain network resources may not be accessible until a new ticket is acquired.
+
+To overcome these issues there is an additional command `become` which takes care of all these aspects. So if you want to switch user, always use:
+
+```bash
+become username
+```