Adding the initial documentation

_pages/docs/comm_interfaces.md

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+---
+layout: single
+title : "Documentation"
+author_profile: false
+excerpt: "Supported communication interfaces"
+header:
+  overlay_color: "#5DADE2"
+permalink: /docs/comm_interfaces/
+sidebar:
+  nav : docs
+---
+{% include base_path %}
+
+The following options can be use with the `--enable-comms=` option to target different communication interfaces:
+
+| `<comm>`      | Description                                  |
+| ------------- | -------------------------------------------- |
+| `none`        | no communications                            |
+| `mpi[-auto]`  | MPI communications                           |
+| `mpi3[-auto]` | MPI communications using [MPI-3 shared memory](https://software.intel.com/sites/default/files/managed/eb/54/An_Introduction_to_MPI-3.pdf) |
+| `shmem `      | Cray SHMEM communications                    |
+
+For `mpi` and `mpi3` the optional `-auto` suffix instructs the `configure` scripts to determine all the necessary compilation and linking flags. This is done by extracting the informations from the MPI wrapper specified in the environment variable `MPICXX` (if not specified `configure` will scan though a list of default names).
+
+{% include paginator.html %}