Add a NERDTreeCWD command to change tree root to CWD
I was going to say that this can easily be done by simply calling :NERDTree but that would create another buffer - which would mess up your nerdtree mirrors
Calling 'NERDTree' for the first time, it does open in the current directory,but after closing and opening it again, it will just using the existed NERD tree which probably not using current directory as root.
Let's say I opened several tabs and use NERDTreeMirror in each tab to make sure I am using only one NERD tree.
If I want change the NERDTree to the the current directory, calling 'NERDTree' would close the mirrored NERDTree window and create a new one which is not what I want. My orignal motive was explained in my answer of Vim: How to synchronize NERDTree with current opened tab file path? at StackExchange network.