Add additional license filenames (#2227)

* Add additional license filenames

Signed-off-by: Colm O hEigeartaigh <coheigea@apache.org>

* add comment about the license list being manually updated

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Colm O hEigeartaigh <coheigea@apache.org>
Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>
Co-authored-by: Alex Goodman <wagoodman@users.noreply.github.com>

internal/licenses/list.go

@@ -3,7 +3,8 @@ package licenses
 import "github.com/anchore/syft/internal"
 
 // all of these taken from https://github.com/golang/pkgsite/blob/8996ff632abee854aef1b764ca0501f262f8f523/internal/licenses/licenses.go#L338
-// which unfortunately is not exported. But fortunately is under BSD-style license.
+// which unfortunately is not exported. But fortunately is under BSD-style license. Take note that this list has
+// been manually updated to include more license filenames (see https://github.com/anchore/syft/pull/2227).
 
 var (
 	FileNames = []string{
@@ -18,6 +19,7 @@ var (
 		"LICENSE",
 		"LICENSE.md",
 		"LICENSE.markdown",
+		"license.txt",
 		"LICENSE.txt",
 		"LICENSE-2.0.txt",
 		"LICENCE-2.0.txt",
@@ -47,6 +49,8 @@ var (
 		"MIT_LICENCE",
 		"UNLICENSE",
 		"UNLICENCE",
+		"AL2.0",
+		"LGPL2.1",
 	}
 
 	FileNameSet = internal.NewStringSet(FileNames...)