Document that for "usual" regex behavior multiline is required

Regular expression users typically expect that matching a `$` in a
multiline string would match the end of current line and not the end
of the string past many lines. This is default behavior in pretty much
every regexp engine: `grep`, `perl`, text editors, you name it… So it
is fair to expect such expectation, so warn a user about necessity to
pass `multiline`

Fixes: #231

Author: Hi-Angel

src/Parsing/String.purs

@@ -195,6 +195,9 @@ match p = do
 
 -- | Compile a regular expression `String` into a regular expression parser.
 -- |
+-- | Note that per JS RegExp semantics matching a single line in a multiline
+-- | string requires passing `multiline` flag rather than `noFlags`.
+-- |
 -- | This function will use the `Data.String.Regex.regex` function to compile
 -- | and return a parser which can be used
 -- | in a `ParserT String m` monad.