diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f411aba
--- /dev/null
+++ b/README.md
@@ -0,0 +1,42 @@
+This is a simple template for creating custom envelopes. Every now and
+then I need to create my own envelopes (e.g. when I am out of the
+bought ones), so this should save me time re-inventing the shapes and cuts.
+
+# Usage
+
+1. Install asymptote
+1. Tweak parameters at the top of `envelope.asy`
+1. `asy envelope`
+1. print `envelope.pdf`
+
+## Parameters explained
+
+- `pgw` and `pgh` are page width and height, respectively. If
+  `force_output_size` is true, these are used to output a document with
+  exact dimensions.
+- `sqsz` is the length of the edge of the bounding square. At this
+  moment, we are always creating envelopes out of a square. (Setting
+  `sqsz = pgw` means that the square will span whole page width.)
+- `envh` and `envw` are the size of the resulting envelope. `envfmt` is
+  the format, for reference and debugging.
+- When `with_labels` is true, the output will contain debugging labels
+  like names of various used points.
+
+# Known bugs
+
+- Undefined behaviour when the envelope does not fit the rectangle (or
+  fits too tightly).
+- Undefined behaviour when the sizes do not follow the ordering
+  invariants (the page must be in portrait orientation, the envelope in
+  landscape)
+- Nobody checks the validity of the config. No safeguards whatsoever.
+
+# License
+
+CC0. This is too trivial to have any creative value. Attribution is
+welcome though.
+
+# Bugs, suggestions, contibutions, patches, discussion, &c.
+
+Please mail me at
+[envelope@pokemon.ledoian.cz](mailto:envelope@pokemon.ledoian.cz).