Updated README in ergodox_infinity keyboard (#1702)

* changed 'infinity' to 'ergodox_infinity' and specified to be in the top-level directory as per recent changes to directory structure of QMK_firmware git repo

* accidently removed '-' in last line of readme

keyboards/ergodox_infinity/readme.md

@@ -3,6 +3,8 @@
 The Infinity is two completely independent keyboards, and needs to be flashed
 for the left and right halves seperately.  To flash them:
 
+  - Make sure you are in the top-level qmk_firmware directory
+
   - Build the firmware with `make ergodox_infinity-keymapname`
 
   - Plug in the left hand keyboard only.
@@ -42,4 +44,5 @@ You have a few options in how you flash the firmware:
 
 - For minor changes such as changing only the keymap without having updated
   any part of the firmware code itself, you can program only the MASTER half.
-  It is safest to program both halves though.
+
+- It is safest to program both halves though.