fix for project instructions (#677)

Fix the instructions to install the copr repo in order to be able to install compat packages.

project-instructions.md

@@ -1,10 +1,14 @@
 For instructions on how to use this repository, consult the [official docs](https://docs.pagure.org/copr.copr/how_to_enable_repo.html#how-to-enable-repo).
 
-It should be enough to enable the copr repository for this project using the following command:
+We need a bit of post-configuration after enabling the copr repository for this project:
 
 ```
-$ dnf install 'dnf-command(copr)'
-$ dnf copr enable -y @fedora-llvm-team/llvm-snapshots
+$ dnf -y install jq envsubst
+$ dnf -y install --skip-broken 'dnf-command(copr)' 'dnf5-command(copr)'
+$ dnf -y copr enable @fedora-llvm-team/llvm-snapshots
+$ repo_file=$(dnf repoinfo --json *llvm-snapshots* | jq -r ".[0].repo_file_path")
+$ distname=$(rpm --eval "%{?fedora:fedora}%{?rhel:rhel}") envsubst '$distname' < $repo_file > /tmp/new_repo_file
+$ cat /tmp/new_repo_file > $repo_file
 ```
 
 Then install `clang` or some of the other packages.