docs: fix and elaborate the nodes field in Linux memory policy

Nodes is required only in some memory policy modes, while some other
modes require that there must be no nodes.

Signed-off-by: Antti Kervinen <[email protected]>

Author: askervin

config-linux.md

@@ -831,7 +831,7 @@ For more information see the [set_mempolicy(2)][set_mempolicy.2] man page.
     * `MPOL_PREFERRED_MANY`
     * `MPOL_LOCAL`
 
-* **`nodes`** *(string, REQUIRED)* - list of memory nodes from which nodemask is constructed to set_mempolicy(2). This is a comma-separated list, with dashes to represent ranges. For example, `0-3,7` represents memory nodes 0,1,2,3, and 7.
+* **`nodes`** *(string, OPTIONAL)* - list of memory nodes from which nodemask is constructed to set_mempolicy(2). This is a comma-separated list, with dashes to represent ranges. For example, `0-3,7` represents memory nodes 0,1,2,3, and 7. Some modes require that there are no nodes, e.g. `MPOL_DEFAULT` and `MPOL_LOCAL`. Others that there is at least one node, e.g. `MPOL_BIND` and `MPOL_INTERLEAVE`. See set_mempolicy(2) for details.
 
 * **`flags`** *(array of strings, OPTIONAL)* - list of flags to use with set_mempolicy(2).