doc: add some prompt for qwfassoc

wfassoc-cdylib/src/lib.rs

@@ -24,17 +24,17 @@ enum Error {
     Program(#[from] wfassoc::highlevel::ProgramError),
 
     /// Error when manipulating with C-style string.
-    #[error("{0}")]
+    #[error("C-Style string FFI error:{0}")]
     CStrFfi(#[from] cstr_ffi::Error),
     /// Error when manipulating with object pool.
-    #[error("{0}")]
+    #[error("object pool error: {0}")]
     ObjectPool(#[from] object_pool::Error),
 
     /// Error occurs when checking enum value
-    #[error("")]
+    #[error("the enumeration value provided to FFI function is out of its range")]
     EnumOutOfRange,
     /// Error when manipulating with poison RwLock
-    #[error("RwLock is poisoning")]
+    #[error("concurrency error: RwLock is poisonous")]
     PoisonRwLock,
 }