Update possible mypy return codes, update documentation

README.markdown

@@ -22,6 +22,7 @@
 2. [Installation](#installation)  
 2.1. [Requirements](#requirements)  
 2.2. [Installing syntastic with Pathogen](#installpathogen)  
+2.3. [Installing syntastic with vim packages](#installvim)  
 3. [Recommended settings](#settings)  
 4. [FAQ](#faq)  
 4.1. [I installed syntastic but it isn't reporting any errors...](#faqinfo)  
@@ -171,6 +172,21 @@ following:
 3. Did the `git clone` of syntastic inside `~/.vim/bundle`
 4. Have permissions to access all of these directories.
 
+<a name="installvim"></a>
+
+### 2.3\. Installing syntatic with vim packages
+
+```
+git clone https://github.com/vim-syntastic/syntastic.git ~/.vim/pack/plugins/start/syntastic.vim
+```
+
+After installing, launch vim and run
+```
+:helptags ~/.vim/pack/plugins/start/syntastic.vim/doc/
+```
+to generate the manual (`:help syntastic`) 
+
+
 <a name="settings"></a>
 
 ## 3\. Recommended settings

syntax_checkers/python/mypy.vim

@@ -32,7 +32,7 @@ function! SyntaxCheckers_python_mypy_GetLocList() dict
     return SyntasticMake({
         \ 'makeprg': makeprg,
         \ 'errorformat': errorformat,
-        \ 'returns': [0, 1],
+        \ 'returns': [0, 1, 2],
         \ 'preprocess': 'mypy' })
 endfunction