Add note about file extensions

1 files changed, 10 insertions, 0 deletions

diff --git a/README.md b/README.md
index 7413894..92e7e26 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,16 @@ Namespaces are always capitalized. I would prefer always lowercase, but
 this actually translates quite well and helps distinguish between types
 and values.
 
+File extensions denote _type_ and indicate to the build system how to
+handle the file. So for example:
+
+- `.hs` is Haskell source code, the build system compiles it
+- `.scm` is Scheme source code, ditto
+- `.org` is an organizational text document, the build system ignores
+  this, but we use them to make plans and such
+- `.jnl` is a journal for accounting, the build system will check our
+  balances, make sure we're profitable
+
 ## Development
 
 To build code, do: