took advantage of tmux 1.8 blocking 'if-shell' to detect '~/.tmux.conf.local'

starting with tmux 1.8, it's an error to source a non existing file

.tmux.conf

@@ -127,7 +127,7 @@ if 'command -v reattach-to-user-namespace' 'bind y run "tmux save-buffer - | rea
 
 # -- user defined --------------------------------------------------------------
 
-source ~/.tmux.conf.local
+if '[ -f ~/.tmux.conf.local ]' 'source ~/.tmux.conf.local'
 
 
 # -- 8< ------------------------------------------------------------------------

README.md

@@ -19,10 +19,6 @@ Installation
     $ rm -rf .tmux
     $ git clone https://github.com/gpakosz/.tmux.git
     $ ln -s .tmux/.tmux.conf
-    $ touch ~/.tmux.conf.local
-
-Note: `tmux` 1.8 doesn't silently ignore sourcing missing files anymore. That's
-why you now have to `touch ~/.tmux.conf.local`.
 
 ### Accessing the Mac OSX clipboard from within tmux sessions