add codespell: config, workflow and have a typo fixed

.codespellrc

@@ -0,0 +1,4 @@
+[codespell]
+skip = .git,*.pdf,*.svg
+# some ad-hoc variables etc
+ignore-words-list = splitted,optin

.github/workflows/codespell.yml

@@ -0,0 +1,22 @@
+---
+name: Codespell
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  codespell:
+    name: Check for spelling errors
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Codespell
+        uses: codespell-project/actions-codespell@v2

src/main/kotlin/HedTagInput.kt

@@ -49,7 +49,7 @@ class HedTagInput(private val tagger: CTagger, private val curField: String, pri
      * Action handler when a character is inserted
      * 1. Get word (HED tag) to which the new character is part of
      * 2. Search and process result
-     *      2.1. If tag exist, show search result in the window below the word, black highlight (overwritting any active red highlight).
+     *      2.1. If tag exist, show search result in the window below the word, black highlight (overwriting any active red highlight).
      *      2.2. If tag doesn't exist, hide result window (if on) and red highlight the word
      */
     override fun insertUpdate(e: DocumentEvent) {