diff --git a/doc/build.md b/doc/build.md
index 7af121f..4026ea0 100644
--- a/doc/build.md
+++ b/doc/build.md
@@ -18,7 +18,21 @@
 
 Then access `http://localhost:8080/` in your browser. The default administrator account is `root` and password is `root`.
 
-Source code modifications are detected and a reloading happens automatically. You can modify the logging configuration by editing `src/main/resources/logback-dev.xml`.
+Source code modifications are detected and a reloading happens automatically.
+You can modify the logging configuration by editing `src/main/resources/logback-dev.xml`.
+
+Note that HttpSession is cleared when auto-reloading happened.
+This is a bit annoying when developing features that requires sign-in.
+You can keep HttpSession even if GitBucket is restarted by enabling this configuration in `build.sbt`:
+https://github.com/gitbucket/gitbucket/blob/d5c083b70f7f3748d080166252e9a3dcaf579648/build.sbt#L292
+
+Or by launching GitBucket with the following command:
+```shell
+sbt '; set Jetty/javaOptions += "-Ddev-features=keep-session" ; ~jetty:start'
+```
+
+Note that this feature serializes HttpSession on the local disk and assigns all requests to the same session
+which means you cannot test multi users behavior in this mode.
 
 Build war file
 --------
@@ -37,7 +51,8 @@
 $ sbt executable
 ```
 
-at the top of the source tree. It generates executable `gitbucket.war` into `target/executable`. We release this war file as release artifact.
+at the top of the source tree. It generates executable `gitbucket.war` into `target/executable`.
+We release this war file as release artifact.
 
 Run tests spec
 ---------