Add section on input devices.

Change-Id: Ib9c4909881df505b11537c28bd08182933a5565a
diff --git a/src/tech/sidebar.md b/src/tech/sidebar.md
index 67ec0a4..3f81124 100644
--- a/src/tech/sidebar.md
+++ b/src/tech/sidebar.md
@@ -3,3 +3,4 @@
 - [Debugging](/tech/debugging/index.html)
 - [Encryption](/tech/encryption/index.html)
 - [Security](/tech/security/index.html)
+- [Input](/tech/input/index.html)