rbenv: add page (#2133)

pages/common/rbenv.md

@@ -0,0 +1,31 @@
+# rbenv
+
+> A tool to easily install Ruby versions and manage application environments.
+
+- Install one or more space-separated versions of Ruby:
+
+`rbenv install {{version(s)}}`
+
+- Display a list of installed versions:
+
+`rbenv versions`
+
+- Use a specific version of Ruby across the whole system:
+
+`rbenv global {{version}}`
+
+- Use a specific version of Ruby for an application/project folder:
+
+`rbenv local {{version}}`
+
+- Show the currently selected Ruby version:
+
+`rbenv version`
+
+- Uninstall a version of Ruby:
+
+`rbenv uninstall {{version}}`
+
+- Display all ruby versions that contain the specified executable:
+
+`rbenv whence {{executable}}`