diff --git a/README.md b/README.md
index a0120ec..a3684e5 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,18 @@
 # pmh7tool
-# pmh7tool
+
+This is a tool to dump, read from, write to PMH7 registers on Lenovo ThinkPad laptops. 
+
+This tool is a part of the coreboot project.
+
+### Usage
+
+	-h, --help:  print help
+	-d, --dump:  hexdump registers
+	-w, --write <addr> <data>:  write <data> to register <addr>
+	-r, --read <addr>:  read from register <addr>
+	-c, --clear-bit <addr> <bit>: clear bit <bit> in register <addr>
+	-s, --set-bit <addr> <bit>: set bit <bit> in register <addr>
+
+# Attention
+
+Writing to PMH7 registers is very dangerous, as you directly manipulate the power rails, enable lines, interrupt lines or something else of the device. **Proceed with caution.**