Doc: proper quoting in vcs_cmds

References #164.

doc/signify.txt

@@ -162,6 +162,13 @@ Modifiers:~
 NOTE: The output format mustn't change, otherwise Sy won't give any reasonable
 results. It's probably wise to start with the respective default values.
 
+NOTE: If your VCS program is not in $PATH and you have to specify an absolute
+path, escape spaces by quoting, e.g.:
+>
+    let g:signify_vcs_cmds = {
+      \ 'git': '"C:\Program Files (x86)\Git\bin\git.exe" --no-color --no-ext-diff -U0 -- %f'
+      \ }
+<
 Default:
 >
     let g:signify_vcs_cmds = {