Include docs of plugins

doc/ft-gitcommit-plugin.txt

@@ -0,0 +1,25 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'git') == -1
+
+GIT COMMIT                                              *ft-gitcommit-plugin*
+
+One command, :DiffGitCached, is provided to show a diff of the current commit
+in the preview window.  It is equivalent to calling "git diff --cached" plus
+any arguments given to the command.
+
+GIT REBASE                                              *ft-gitrebase-plugin*
+
+In a gitrebase filetype buffer, the following commands are provided:
+
+  `:Pick`     Changes the cursor line to a `pick` line.
+  `:Squash`   Changes the cursor line to a `squash` line
+  `:Edit`     Changes the cursor line to an `edit` line
+  `:Reword`   Changes the cursor line to a `reword` line
+  `:Fixup`    Changes the cursor line to a `fixup` line
+  `:Drop`     Changes the cursor line to a `drop` line
+  `:Cycle`    Cycles between the first 5 gitrebase commands
+
+To make the `:Cycle` command more useful, it might be mapped, e.g. >
+  nnoremap <buffer> <silent> S :Cycle<CR>
+<
+
+endif