Added README.

From here: http://www.vim.org/scripts/script.php?script_id=664

Author: duff

README

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+You can use the scratch plugin to create a temporary scratch buffer to store 
+and edit text that will be discarded when you quit/exit vim. The contents 
+of the scratch buffer are not saved/stored in a file. 
+
+Installation 
+
+1. Copy the scratch.vim plugin to the $HOME/.vim/plugin directory. Refer to 
+   the following Vim help topics for more information about Vim plugins: 
+
+      :help add-plugin 
+      :help add-global-plugin 
+      :help runtimepath 
+
+2. Restart Vim. 
+
+Usage 
+
+You can use the following command to open/edit the scratch buffer: 
+
+      :Scratch 
+
+To open the scratch buffer in a new split window, use the following command: 
+
+      :Sscratch 
+
+When you close the scratch buffer window, the buffer will retain the 
+contents. You can again edit the scratch buffer by openeing it using one of 
+the above commands. There is no need to save the scatch buffer. 
+
+When you quit/exit Vim, the contents of the scratch buffer will be lost. 
+You will not be prompted to save the contents of the modified scratch 
+buffer. 
+
+You can have only one scratch buffer open in a single Vim instance. If the 
+current buffer has unsaved modifications, then the scratch buffer will be 
+opened in a new window 
+ 
+install details
+1. Copy the scratch.vim plugin to the $HOME/.vim/plugin directory. 
+2. Restart Vim
+