docs: add AFS from home page

Signed-off-by: Nicolas Froger <nico@cri.epita.fr>

docs/from_home/afs.md

+# Accessing the AFS from home
+
+CRI's AFS is accessible from outside the school's network using the SSH Gate.
+
+## Setup
+
+Add the following to your SSH config (`~/.ssh/config`):
+```
+Host ssh.cri.epita.fr
+	GSSAPIAuthentication yes
+	GSSAPIDelegateCredentials yes
+```
+
+## Procedure
+
+Run `kinit -f login@CRI.EPITA.FR` (replace `login` with your login) and type in
+your CRI password when asked.
+
+If you are using a SSH agent, make sure to disable it temporarly in your current
+shell. This can be done by running `unset SSH_AUTH_SOCK`.
+
+## Browse interactively your AFS
+
+Run `sftp login@ssh.cri.epita.fr`, a SFTP prompt should show up. You can refer
+to the `sftp(1)` man page to get familiar with the tool.
+
+If your login is `login`, your files are located in
+`/afs/cri.epita.fr/user/l/lo/login/u/`. 
+
+```shell
+$ sftp marin.hannache@ssh.cri.epita.fr
+Connected to ssh.cri.epita.fr.
+sftp> cd /afs/cri.epita.fr/user/m/ma/marin.hannache/u/
+sftp> ls -la
+drwxr-xr-x    3 marin.hannache 8000         2048 Sep 14 05:55 .
+drwxrwxrwx    3 marin.hannache 8000         2048 Sep 14  2017 ..
+drwxr-xr-x    9 marin.hannache 8000         2048 Oct 29 23:55 .confs
+```
+
+If you get a `Permission denied` error when trying to access to your files, you
+very likely made a mistake in your setup. Make sure you did not connect using
+your SSH Agent or through your SSH keys.
+
+## Mounting the AFS
+
+You can also mount the AFS to your Linux system (or the CRI VM) in a very
+similar way as it is done at school.
+
+This can be done using the following commands:
+
+```shell
+$ mkdir -p afs
+$ sshfs -o reconnect login@ssh.cri.epita.fr:/afs/cri.epita.fr/user/l/lo/login/u/ afs
+```
+
+!!! warning
+    The files will not be accessible after the Kerberos ticket expires (usually
+    after a few days). If this happens, ask for a new ticket by running
+    `kinit -f login@CRI.EPITA.FR` and unmount the afs folder by running
+    `umount afs/`. You can then mount it again with the same `sshfs` command as
+    previously.

mkdocs.yml

@@ -29,6 +29,7 @@ nav:
       - 'from_home/vm/common_issues.md'
       - 'from_home/vm/tips.md'
     - Disk/USB Installation: 'from_home/bare-metal.md'
+    - AFS: 'from_home/afs.md'
   - Contributing:
     - 'map_contributing.md'
     - 'doc_contributing.md'