skysh: add information on history file location

Author: ohsayan

docs/3.using-repl.md

@@ -35,7 +35,8 @@ You can also run queries like: `inspect global` to see available global system i
 
 :::info Quick notes
 
-- The REPL currently stores history in the `.sky_history` file. If you want to remove history, you can simply delete the file
+- The REPL stores all command history in a file located at `$HOME/.sky_history` (here `$HOME` represents your home directory)
+- If you wish to change where the REPL stores the history file, set the `SKYSH_HISTORY_FILE` environment variable to your preferred path
 - The REPL will automatically parameterize queries. Don't worry about what this means; you'll learn about it ahead.
 - The REPL applies custom formatting to `DDL` queries. For example, even though  `inspect global` returns a JSON as a string,
 the REPL formats it and outputs it without quotes, to improve readability