add twisted to RTD requirements so the docs for effect.twisted can be built

radix · radix · commit 7f5001c2a19e · 2015-05-06T09:50:10.000-05:00
diff --git a/rtd-requirements.txt b/rtd-requirements.txt
@@ -1,2 +1,3 @@
 # requirements for Read The Docs
 alabaster
+twisted

Original file line number	Diff line number	Diff line change
`@@ -1,2 +1,3 @@`
`1`	`1`	`# requirements for Read The Docs`
`2`	`2`	`alabaster`
	`3`	`+twisted`