Add note about sefcontext doing no restorecon (#39076)

* Add note about sefcontext doing no restorecon

To someone like me who is relatively new to SELinux, setting the
"reload" option to yes might suggest that a restorecon is automatically
executed after the semanage call, making the new file context effective
immediately. I have found out that this is not the case and would like
to clarify this to others.

+label: docsite_pr

* Replace note by one suggested by reviewer

Reviewer dagwieers suggested a better notice text during review of my
original one, giving recommendations about what to do to actually get
the newly chosen SELinux context applied to the file.

lib/ansible/modules/system/sefcontext.py

@@ -53,6 +53,10 @@ options:
     default: 'yes'
 notes:
 - The changes are persistent across reboots
+- The M(sefcontext) module does not modify existing files to the new
+  SELinux context(s), so it is advisable to first create the SELinux
+  file contexts before creating files, or run C(restorecon) manually
+  for the existing files that require the new SELinux file contexts.
 requirements:
 - libselinux-python
 - policycoreutils-python