feat(Documentation/cloud-config): add section about oem-release

We need to have cloud-config render a file about itself that can be
easily parsed and used by the rest of the system. Essentially just copy
the os-release format.

Documentation/cloud-config.md

@@ -13,7 +13,12 @@ Provided public SSH keys will be authorized for the `core` user.
 The keys will be named "coreos-cloudinit" by default.
 Override this with the `--ssh-key-name` flag when calling `coreos-cloudinit`.
 
-#### users
+### hostname
+
+The provided value will be used to set the system's hostname.
+This is the local part of a fully-qualified domain name (i.e. `foo` in `foo.example.com`).
+
+### users
 
 Add or modify users with the `users` directive by providing a list of user objects, each consisting of the following fields.
 Each field is optional and of type string unless otherwise noted.
@@ -41,14 +46,58 @@ The following fields are not yet implemented:
 
 ##### Generating a password hash
 
-You can generate a safe hash via:
+Generating a safe hash is important to the security of your system.  Currently with updated tools like [oclhashcat](http://hashcat.net/oclhashcat/) simplified hashes like md5crypt are trivial to crack on modern GPU hardware.  You can generate a "safer" hash (read: not safe, never publish your hashes publicly) via:
 
+###### On Debian/Ubuntu (via the package "whois")
     mkpasswd --method=SHA-512 --rounds=4096
 
-Using a higher number of rounds will help create more secure passwords, but given enough time, password hashes can be reversed.
+###### With OpenSSL (note: this will only make md5crypt.  While better than plantext it should not be considered fully secure)
+    openssl passwd -1
+
+###### With Python (change password and salt values)
+    python -c "import crypt, getpass, pwd; print crypt.crypt('password', '\$6\$SALT\$')"
+
+###### With Perl (change password and salt values)
+    perl -e 'print crypt("password","\$6\$SALT\$") . "\n"'
+
+Using a higher number of rounds will help create more secure passwords, but given enough time, password hashes can be reversed.  On most RPM based distributions there is a tool called mkpasswd available in the `expect` package, but this does not handle "rounds" nor advanced hashing algorithms. 
+
+### write_files
+
+Inject an arbitrary set of files to the local filesystem.
+Provide a list of objects with the following attributes:
+
+- **path**: Absolute location on disk where contents should be written
+- **content**: Data to write at the provided `path`
+- **permissions**: String representing file permissions in octal notation (i.e. '0644')
+- **owner**: User and group that should own the file written to disk. This is equivalent to the `<user>:<group>` argument to `chown <user>:<group> <path>`.
 
 ## Custom cloud-config Parameters
 
+### coreos.oem
+
+These fields are borrowed from the [os-release spec][os-release] and repurposed
+as a way for cloud-init to know about the OEM partition on this machine.
+
+- **id**: A lower case string identifying the oem.
+- **version-id**: A lower case string identifying the version of the OEM. Example: `168.0.0`
+- **name**: A name without the version that is suitable for presentation to the user.
+- **home-url**: Link to the homepage of the provider or OEM.
+- **bug-report-url***: Link to a place to file bug reports about this OEM partition.
+
+cloudinit must render these fields down to an /etc/oem-release file on disk in the following format:
+
+```
+NAME=Rackspace
+ID=rackspace
+VERSION_ID=168.0.0
+PRETTY_NAME="Rackspace Cloud Servers"
+HOME_URL="http://www.rackspace.com/cloud/servers/"
+BUG_REPORT_URL="https://github.com/coreos/coreos-overlay"
+```
+
+[os-release]: http://www.freedesktop.org/software/systemd/man/os-release.html
+
 ### coreos.etcd.discovery_url
 
 The value of `coreos.etcd.discovery_url` will be used to discover the instance's etcd peers using the [etcd discovery protocol][disco-proto]. Usage of the [public discovery service][disco-service] is encouraged.
@@ -129,3 +178,19 @@ users:
 	ssh-authorized-keys:
 	  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...
 ```
+
+### Inject configuration files
+
+```
+#cloud-config
+
+write_files:
+  - path: /etc/hosts
+    contents: |
+      127.0.0.1    localhost
+      192.0.2.211  buildbox
+  - path: /etc/resolv.conf
+    contents: |
+      nameserver 192.0.2.13
+      nameserver 192.0.2.14
+```

coreos-cloudinit.go

@@ -10,7 +10,7 @@ import (
 	"github.com/coreos/coreos-cloudinit/cloudinit"
 )
 
-const version = "0.1.2"
+const version = "0.1.2+git"
 
 func main() {
 	var userdata []byte