rbash: add page (#1634)

pages/common/rbash.md

@@ -0,0 +1,20 @@
+# rbash
+
+> Restricted Bash shell.
+> Similar to the `bash` shell with some restrictions like changing directories with `cd`, setting/unsetting of PATH, ENV variables and others.
+
+- Start rbash:
+
+`rbash`
+
+- Execute a command:
+
+`rbash -c "{{command}}"`
+
+- Run commands from a file:
+
+`rbash {{file.sh}}`
+
+- Print the version information of rbash:
+
+`rbash --version`