doc: mappings use <LocalLeader> prefix, not <Leader>

If you have changed the mapleader/<Leader> key in vim, the plugin
mappings do not work. This is because the plugin actually uses
<LocalLeader>, not <Leader> like the documentation says. Fix
documentation.
doc: fix tex2dot => dot2tex typos
Merge pull request #7 from bjornfor/doc-fixes

Doc fixes