add user doc

Signed-off-by: Lantao Jin <[email protected]>

docs/user/ppl/general/comments.rst

@@ -0,0 +1,44 @@
+========
+Comments
+========
+
+.. rubric:: Table of contents
+
+.. contents::
+   :local:
+   :depth: 2
+
+
+Comments are not evaluated texts. PPL supports both line comments and block comments.
+
+Line Comments
+-------------
+Line comments begin with two slashes ( // ) and end with a new line.
+
+Example::
+
+    os> source=accounts | top gender // finds most common gender of all the accounts
+    fetched rows / total rows = 2/2
+    +----------+
+    | gender   |
+    |----------|
+    | M        |
+    | F        |
+    +----------+
+
+Block Comments
+--------------
+Block comments begin with a slash followed by an asterisk ( /\* ) and end with an asterisk followed by a slash ( \*/ ).
+
+Example::
+
+    os> source=accounts | dedup 2 gender /* dedup the document with gender field keep 2 duplication */ | fields account_number, gender
+    fetched rows / total rows = 3/3
+    +------------------+----------+
+    | account_number   | gender   |
+    |------------------+----------|
+    | 1                | M        |
+    | 6                | M        |
+    | 13               | F        |
+    +------------------+----------+
+