treewide: add missing option descriptions

The new options processor errors out on these by default, and it's
good for every option to have documentation in general.

modules/programs/aerc-accounts.nix

@@ -18,18 +18,22 @@ let
           token_endpoint = mkOption {
             type = nullOr str;
             default = null;
+            description = lib.mdDoc "The OAuth2 token endpoint.";
           };
           client_id = mkOption {
             type = nullOr str;
             default = null;
+            description = lib.mdDoc "The OAuth2 client identifier.";
           };
           client_secret = mkOption {
             type = nullOr str;
             default = null;
+            description = lib.mdDoc "The OAuth2 client secret.";
           };
           scope = mkOption {
             type = nullOr str;
             default = null;
+            description = lib.mdDoc "The OAuth2 requested scope.";
           };
         };
       });

modules/programs/papis.nix

@@ -71,6 +71,7 @@ in {
           };
         };
       }));
+      description = "Attribute set of papis libraries.";
     };
   };
 

modules/programs/thunderbird.nix

@@ -207,6 +207,7 @@ in {
               };
             };
           }));
+        description = "Attribute set of Thunderbird profiles.";
       };
 
       settings = mkOption {