Create a short markdown readme for crates.io

Cargo.lock

@@ -1,6 +1,6 @@
 [root]
 name = "just"
-version = "0.3.2"
+version = "0.3.3"
 dependencies = [
  "ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "atty 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",

Cargo.toml

@@ -1,11 +1,11 @@
 [package]
 name        = "just"
-version     = "0.3.2"
+version     = "0.3.3"
 description = "🤖 Just a command runner"
 authors     = ["Casey Rodarmor <casey@rodarmor.com>"]
 license     = "WTFPL OR MIT OR Apache-2.0"
 homepage    = "https://github.com/casey/just"
-readme      = "README.asc"
+readme      = "crates-io-readme.md"
 
 [dependencies]
 ansi_term     = "^0.9.0"

crates-io-readme.md

@@ -0,0 +1,22 @@
+`just` is a handy way to save and run project-specific commands.
+
+Commands are stored in a file called `justfile` or `Justfile` with syntax inspired by `make`:
+
+```make
+build:
+    cc *.c -o main
+
+# test everything
+test-all: build
+    ./test --all
+
+# run a specific test
+test TEST: build
+    ./test --test {{TEST}}
+```
+
+`just` produces detailed error messages and avoids `make`'s idiosyncrasies, so debugging a justfile is easier and less surprising than debugging a makefile.
+
+It works on Linux, MacOS, and Windows.
+
+Read more on [GitHub](https://github.com/casey/just).