devtools: Add codespell to pre-commit.

Includes default config file and an initial word list to ignore.

.codespellignore

@@ -0,0 +1,3 @@
+connectd
+crate
+mut

.codespellrc

@@ -0,0 +1,4 @@
+[codespell]
+
+count = true
+ignore-words = .codespellignore

.pre-commit-config.yaml

@@ -18,6 +18,14 @@ repos:
     - id: shellcheck
       args: [ -fgcc ]
 
+- repo: https://github.com/codespell-project/codespell
+  rev: v2.3.0
+  hooks:
+    - id: codespell
+      description: Checks for common misspellings.
+      exclude: ccan|contrib|tests/fuzz/corpora
+      stages: [ manual ]
+
 - repo: local
   hooks:
     # Reimplementation of `make check-amount-access` for pygrep.