lintian: Add explicit source format and override

Change-Id: I1004643bf4fdd11ee4d2d350331c9dce5488ba7c
diff --git a/debian/lintian-overrides b/debian/lintian-overrides
new file mode 100644
index 0000000..d391bed
--- /dev/null
+++ b/debian/lintian-overrides
@@ -0,0 +1 @@
+mendel-keyring: package-installs-apt-keyring etc/apt/trusted.gpg.d/mendel-keyring.gpg
diff --git a/debian/source/format b/debian/source/format
new file mode 100644
index 0000000..d3827e7
--- /dev/null
+++ b/debian/source/format
@@ -0,0 +1 @@
+1.0