feat(nvim): Add astronvim configuration

Signed-off-by: Noah Knegt <git@noahknegt.com>

.config/nvim/selene.toml

@@ -0,0 +1,8 @@
+std = "neovim"
+
+[rules]
+global_usage = "allow"
+if_same_then_else = "allow"
+incorrect_standard_library_use = "allow"
+mixed_table = "allow"
+multiple_statements = "allow"