Autogenerate yadm.md after new jinja functionality

yadm.md

@@ -50,11 +50,12 @@
               The config command is not passed directly through.  Instead  use
               the gitconfig command (see below).
 
-       alt    Create  symbolic links for any managed files matching the naming
-              rules describe in the ALTERNATES section.  It is usually  unnec-
-              essary  to  run  this  command,  as yadm automatically processes
-              alternates by default.  This automatic behavior can be  disabled
-              by setting the configuration yadm.auto-alt to "false".
+       alt    Create  symbolic  links and process jinja templates for any man-
+              aged files matching the naming rules describe in the  ALTERNATES
+              section.  It is usually unnecessary to run this command, as yadm
+              automatically processes alternates by default.   This  automatic
+              behavior can be disabled by setting the configuration yadm.auto-
+              alt to "false".
 
        bootstrap
               Execute $HOME/.yadm/bootstrap if it exists.
@@ -320,6 +321,38 @@
        ridden using the configuration options  local.os,  local.hostname,  and
        local.user.
 
+       If  envtpl  (  pip install envtpl  )  is available, you can also create
+       jinja templates (http://jinja.pocoo.org/) which will  transformed  into
+       real files.  yadm will treat files ending in
+
+        ##yadm_tmpl
+
+       as  jinja templates. During processing, the following variables are set
+       according to the above rules:
+
+        YADM_CLASS
+        YADM_OS
+        YADM_HOSTNAME
+        YADM_USER
+
+       E.g. a file 'whatever##yadm_tmpl' with the following content
+
+        {% if YADM_USER == 'harvey' -%}
+        config={{YADM_CLASS}}-{{ YADM_OS }}
+        {% else -%}
+        config=dev-whatever
+        {% endif -%}
+
+       would output a file with the follwing content, if the username would be
+       'harvey'
+
+        config=work-Linux
+
+       and the following otherwise:
+
+        config=dev-whatever
+
+
 
 ## ENCRYPTION
        It  can  be  useful to manage confidential files, like SSH or GPG keys,