help: set: Clarify strings must be in quotes

Issue: https://tree.taiga.io/project/jktjkt-netconf-cli/issue/231
Change-Id: Icc79e3134e8bd6e169bba101f826561f641d368b
diff --git a/src/ast_commands.hpp b/src/ast_commands.hpp
index d0a3f3e..0d7a476 100644
--- a/src/ast_commands.hpp
+++ b/src/ast_commands.hpp
@@ -116,10 +116,12 @@
     set <path_to_leaf> <value>
 
     Sets the leaf specified by <path_to_leaf> to <value>.
+    Values of type string must be enclosed in quotation marks (" or ').
 
     Usage:
-        /> set /module:leaf 123
-        /> set /module:leaf abc)";
+        /> set /module:someNumber 123
+        /> set /module:someString 'abc'
+        /> set /module:someString "abc")";
     bool operator==(const set_& b) const;
     dataPath_ m_path;
     leaf_data_ m_data;