Refactor Wording, few details on syntax in readme

Closes remarkjsGH-79.

packages/remark-math/readme.md

@@ -139,9 +139,10 @@ If you turn this off, you can still use two or more dollars for text math.
 ## Syntax
 
 This plugin applies a micromark extensions to parse the syntax.
-That basically follows how code works in markdown, except that dollars (`$`)
-are used instead of backticks (`` ` ``), and that two dollars instead of 3 is
-enough for blocks.
+The syntax basically follows how code works in markdown, except that dollars (`$`)
+are used instead of backticks (`` ` ``) and that 2 or more dollars instead of 3
+or more backticks is enough for blocks.
+
 See its readme for parse details:
 
 *   [`micromark-extension-math`](https://github.com/micromark/micromark-extension-math#syntax)
@@ -150,6 +151,17 @@ See its readme for parse details:
 > That means escapes don’t work inside math but you can use more dollars around
 > the math instead: `$$\raisebox{0.25em}{$\frac a b$}$$`
 
+> 👉 **Note**: Like code, the difference between “inline” and “block”,
+> is in the line endings:
+> 
+> ```markdown
+> $$inline$$
+> 
+> $$
+> block
+> $$
+> ```
+
 ## HTML
 
 This plugin integrates with [`remark-rehype`][remark-rehype].