diff --git a/README.md b/README.md
index ab86d5e..3118681 100644
--- a/README.md
+++ b/README.md
@@ -7,8 +7,8 @@
 If you're running Ubuntu Linux:
 
     sudo apt install make python3-pip
-    pip3 install -U pip setuptools
-    pip3 install -U sphinx
+    pip3 install -U pip
+    pip3 install -r requirements.txt
 
 If you're running macOS or another operating system, see the instructions at https://www.sphinx-doc.org/en/master/usage/installation.html
 
@@ -18,7 +18,7 @@
 
     make html
 
-And a set of HTML pages will be generated under `_build/html`.
+And a set of HTML pages will be generated inside `_build/html`.
 
 You can also type:
 
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..c452ba1
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+Sphinx~=4.0