lvalue and rvalue should be documented as well

shepmaster · web-flow · commit 738ad2948e97 · 2018-09-18T12:04:50.000-04:00
diff --git a/reference/src/introduction.md b/reference/src/introduction.md
@@ -8,5 +8,7 @@
 * *niche*
 * *layout*
 * *tag*
+* *rvalue*
+* *lvalue*
 
 ## Unsafe abstraction
