scripts: clean up build environment launch scripts

- With a privileged container (which makes the Bazel sandbox work), the SELinux
  trick doesn't work anyway. Replace it by a `z` modifier which tells podman to
  set the right SELinux context on systems that have it.

- Do not fail if IntelliJ is absent.

Test Plan: works on my machineā„¢

X-Origin-Diff: phab/D758
GitOrigin-RevId: b9020bdd54fccde222872ca609ee79b1805dd479
diff --git a/README.md b/README.md
index d549eba..6fb8def 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@
 
 ## Environment
 
-Our build environment required a working podman or docker environment. 
+Our build environment requires a working Podman binary (your distribution should have one).
 
 #### Usage