check REUSE as part of tox

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

tox.ini

@@ -5,7 +5,7 @@
 
 [tox]
 isolated_build = true
-envlist = begin,py39,py310,py311,coverage,bandit,lint
+envlist = begin,py39,py310,py311,coverage,bandit,lint,reuse
 
 [testenv]
 allow_externals = pytest, coverage
@@ -57,6 +57,11 @@ commands =
     mypy gp2040ce_bintools
     - flake8 --disable-noqa --ignore= --select=E,W,F,C,D,A,G,B,I,T,M,DUO
 
+[testenv:reuse]
+# check license documentation
+commands =
+    reuse lint
+
 [coverage:paths]
 source =
     ./