doc fix: use PODCONFIG_PATH for physical pod

Change-Id: Ic15818363bba75d9df37ba049872d53e610c43df
diff --git a/docs/install_physical.md b/docs/install_physical.md
index 28da37c..7df96a9 100644
--- a/docs/install_physical.md
+++ b/docs/install_physical.md
@@ -326,7 +326,7 @@
 
 ```
 cd ~/cord/build && \
-make PODCONFIG={YOUR_PODCONFIG_FILE.yml} config
+make PODCONFIG_PATH={PATH_TO_YOUR_PODCONFIG_FILE.yml} config
 ```
 
 The process generates a set of files in `~/cord/build/genconfig`