envsetup.sh : add help text for sepgrep and mangrep commands

Change-Id: Iac3942da05c1803039b9fcf15fee1fc0e0f4efda
diff --git a/envsetup.sh b/envsetup.sh
index 45c4067..531ffd9 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -14,6 +14,8 @@
 - ggrep:   Greps on all local Gradle files.
 - jgrep:   Greps on all local Java files.
 - resgrep: Greps on all local res/*.xml files.
+- mangrep: Greps on all local AndroidManifest.xml files.
+- sepgrep: Greps on all local sepolicy files.
 - sgrep:   Greps on all local source files.
 - godir:   Go to the directory containing a file.