Update README.textile
Add upgrade command to docs. I canceled the prompt once and went hunting for this so I could upgrade.
Diff
1diff --git a/README.textile b/README.textile
2index 5f80674992f1bdecce282f749081a015249510c8..1916d9f4e07f65a631f7c7306b20c9ae1f739369 100644
3--- a/README.textile
4+++ b/README.textile
5@@ -72,6 +72,8 @@ To disable updates entirely, put this in your ~/.zshrc
6 7 @DISABLE_AUTO_UPDATE=true@
8 9+To upgrade directly from the command line, just run @upgrade_oh_my_zsh@
10+
11 h3. Uninstalling
1213 If you want to uninstall it, just run @uninstall_oh_my_zsh@ from the command line and it'll remove itself and revert you to bash (or your previous zsh config).