Adds missing doc for syscalls (#1452)

* Add missing syscall documentation

* Add missing space lua documentation

plug-api/syscalls/markdown.ts

@@ -19,6 +19,11 @@ export function renderParseTree(tree: ParseTree): Promise<string> {
   return syscall("markdown.renderParseTree", tree);
 }
 
+/**
+ * Expands custom markdown Lua directives and transclusions into plain markdown
+ * @param tree the parse tree
+ * @returns the expaneded markdown
+ */
 export function expandMarkdown(tree: ParseTree): Promise<ParseTree> {
   return syscall("markdown.expandMarkdown", tree);
 }