add missing license-header.txt for pre-commit hook

Author: adambagley

.gitignore

@@ -67,7 +67,6 @@ sw/apps/*/sw.S
 # Vivado
 *.jou
 *.log
-*.txt
 *.str
 .Xil/
 fpga/build/*/work*

.license-header.txt

@@ -0,0 +1,13 @@
+   Copyright 2026 Two Sigma Open Source, LLC
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.