[Config] Capitalize MUST in config.md

"must" --> "MUST" for RFC 2119 compliance

This replaces PR opencontainers#403 which required a rebase

Signed-off-by: Rob Dolin <RobDolin@microsoft.com>

config.md

@@ -87,8 +87,8 @@ See links for details about [mountvol](http://ss64.com/nt/mountvol.html) and [Se
 
 * **`terminal`** (bool, optional) specifies whether you want a terminal attached to that process. Defaults to false.
 * **`cwd`** (string, required) is the working directory that will be set for the executable. This value MUST be an absolute path.
-* **`env`** (array of strings, optional) contains a list of variables that will be set in the process's environment prior to execution. Elements in the array are specified as Strings in the form "KEY=value". The left hand side must consist solely of letters, digits, and underscores `_` as outlined in [IEEE Std 1003.1-2001](http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html).
-* **`args`** (array of strings, required) executable to launch and any flags as an array. The executable is the first element and must be available at the given path inside of the rootfs. If the executable path is not an absolute path then the search $PATH is interpreted to find the executable.
+* **`env`** (array of strings, optional) contains a list of variables that will be set in the process's environment prior to execution. Elements in the array are specified as Strings in the form "KEY=value". The left hand side MUST consist solely of letters, digits, and underscores `_` as outlined in [IEEE Std 1003.1-2001](http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html).
+* **`args`** (array of strings, required) executable to launch and any flags as an array. The executable is the first element and MUST be available at the given path inside of the rootfs. If the executable path is not an absolute path then the search $PATH is interpreted to find the executable.
 
 For Linux-based systems the process structure supports the following process specific fields:
 
@@ -189,8 +189,8 @@ _Note: For Solaris, uid and gid specify the uid and gid of the process inside th
 
 ## Platform
 
-* **`os`** (string, required) specifies the operating system family this image must run on. Values for os must be in the list specified by the Go Language document for [`$GOOS`](https://golang.org/doc/install/source#environment).
-* **`arch`** (string, required) specifies the instruction set for which the binaries in the image have been compiled. Values for arch must be in the list specified by the Go Language document for [`$GOARCH`](https://golang.org/doc/install/source#environment).
+* **`os`** (string, required) specifies the operating system family this image MUST run on. Values for os MUST be in the list specified by the Go Language document for [`$GOOS`](https://golang.org/doc/install/source#environment).
+* **`arch`** (string, required) specifies the instruction set for which the binaries in the image have been compiled. Values for arch MUST be in the list specified by the Go Language document for [`$GOARCH`](https://golang.org/doc/install/source#environment).
 
 ### Example