add how to install `pip`
diff --git a/doc/readme.md b/doc/readme.md
index 63a2c80..9b1349d 100644
--- a/doc/readme.md
+++ b/doc/readme.md
@@ -21,6 +21,9 @@
 ```
 
 ### Creating a virtualenv environment for documnet build
+
+If `pip` is not installed, you need to install it first by referring to the link: https://pip.pypa.io/en/stable/installing/
+
 ```
 pip install virtualenv