add meta profiles doc

docs/howto/group-hosts.md

@@ -0,0 +1,58 @@
+# Group hosts in config and meta profiles
+
+Let's consider the situation where you have multiple hosts from different distros and you
+want an easy way to structure your config file nicely but also simplify the use
+of templates (since multiple hosts in the same distro would share the same configs parts -
+or if branch in templates).
+
+You define two types of profiles:
+
+* **Meta profiles**: for example for distros it would be something like `os_arch`, `os_debian` and so on.
+  These are never directly used for installing dotfiles but instead included by other profiles.
+* **Host profiles** (defaults to hostnames): the usual `home`, `office`, etc
+
+Each *Host profile* would include a *meta profile* and inherit all its dotfiles as well as
+it variables. For example in the *meta profile* you would define variables like `distro: debian`
+that you could use in your templates with `{%@@ if distro == "debian" @@%}` to target all
+profiles that inherit from the same *meta profile*.
+
+```yaml
+profiles:
+  meta_base:
+    dotfiles:
+    - f_zshrc
+    - f_zshrc
+  os_arch:
+    variables:
+      distro: arch
+    include:
+    - meta-base
+  os_debian:
+    variables:
+      distro: debian
+    include:
+    - meta-base
+  home:
+    include:
+    - os_arch
+    dotfiles:
+    - f_vimrc
+  office:
+    include:
+    - os_debian
+    dotfiles:
+    - f_something
+```
+
+You then have the opportunity in your templates to do the following
+that would select the if branch for all profiles inheriting from
+a specific *meta profile*.
+```
+# zsh-syntax-highlighting
+# https://github.com/zsh-users/zsh-syntax-highlighting
+{%@@ if distro == "arch" @@%}
+source /usr/share/zsh/plugins/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
+{%@@ elif distro == "debian" @@%}
+source /usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
+{%@@ endif @@%}
+```