Make it clear that jiri should be in PATH

Change-Id: I146e2adb93c0ea5f395c79d34c0435ace436d00c
diff --git a/getting_source.md b/getting_source.md
index a6b315a..c531c2b 100644
--- a/getting_source.md
+++ b/getting_source.md
@@ -24,8 +24,9 @@
 
 This script will bootstrap a development environment for the given layer in a
 directory named after the layer. Upon success, the script should print a message
-recommending that you add the `.jiri_root/bin` directory to your PATH (which
-you should do).
+recommending that you add the `.jiri_root/bin` directory to your PATH. Adding
+**jiri** to your PATH is strongly recommended and is assumed by other parts of the
+Fuchsia toolchain.
 
 ### Working without altering your PATH
 
@@ -45,4 +46,5 @@
 ln -s `pwd`/scripts/fx ~/bin
 ```
 
-or just run the tool directly as `scripts/fx`.
+or just run the tool directly as `scripts/fx`. Make sure you have **jiri** in
+your PATH.