Edit approval workflow and update miscellanea

.github/workflows/main.yml

@@ -40,3 +40,12 @@ jobs:
           toolchain: stable
       - run: rustup component add rustfmt
       - run: cargo fmt --check
+
+  macrokata-checks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+      - run: cargo run --bin macrokata -- check-all

CONTRIBUTING.md

@@ -0,0 +1,14 @@
+# Contributing to Macrokata
+
+Thank you for your interest in helping with MacroKata.
+
+These instructions are probably incomplete (feel free to PR to add to them)!
+
+## What are `solution.diff` files?
+
+Since we have to maintain two separate files (the starter code, and the solution code),
+it's very easy to make a change in one that affects the other.
+
+Therefore, `solution.diff` files describe what the correct diff is between a starter
+code and solution code. If you intentionally change this, use the `macrokata update-diff`
+command to update the file. Part of any PR will be checking that this diff is sane.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "macrokata"
-version = "0.2.0"
+version = "0.2.1"
 edition = "2021"
 default-run = "macrokata"
 
@@ -109,3 +109,4 @@ path = "exercises/12_hygienic_macros/solutions/main.rs"
 atty = "0.2.14"
 clap = { version = "4.0.26", features = ["derive"] }
 imara-diff = "0.1.5"
+glob = "0.3.0"