project-template: use .md extension for LICENSE and NOTICE

This allows proper integration with tools such as Gitbook.

Signed-off-by: Santiago M. Mola <santi@mola.io>

Author: smola

engineering/documents/apache/LICENSE

@@ -1 +1 @@
-../../project-template/LICENSE.apache
+../project-template/LICENSE.md.apache

engineering/documents/cc-by-sa/LICENSE

@@ -1 +1 @@
-../../project-template/LICENSE.cc-by-sa
+../project-template/LICENSE.md.cc-by-sa

engineering/documents/gpl/LICENSE

@@ -1 +1 @@
-../../project-template/LICENSE.gpl
+../project-template/LICENSE.md.gpl

engineering/project-template/LICENSE.apache renamed to engineering/project-template/LICENSE.md.apache

@@ -83,16 +83,16 @@ There's a choice between the following three licenses:
 You will find more info about what license to choose at: https://github.com/src-d/guide/blob/master/engineering/licensing.md
 ```
 
-Apache License Version 2.0, see [LICENSE](LICENSE).
+Apache License Version 2.0, see [LICENSE.md](LICENSE.md).
 
 ```
 or
 ```
 
-GPL v3.0, see [LICENSE](LICENSE).
+GPL v3.0, see [LICENSE.md](LICENSE.md).
 
 ```
 or
 ```
 
-This work is licensed under a Creative Commons Attribution 4.0 International License. See [LICENSE](LICENSE).
+This work is licensed under a Creative Commons Attribution 4.0 International License. See [LICENSE.md](LICENSE.md).