Check-in gemmini headers instead of submodule

gemmini/rocc-software/CONTRIBUTING.md

@@ -0,0 +1,46 @@
+All contributors must agree to the Developer Certificate of Origin Version 1.1. (DCO 1.1) by signing their commits with:
+
+```
+DCO 1.1 Signed-off-by: [NAME] <[EMAIL]>
+```
+
+The full text of the DCO 1.1 is as follows:
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+660 York Street, Suite 102,
+San Francisco, CA 94110 USA
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+have the right to submit it under the open source license
+indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+of my knowledge, is covered under an appropriate open source
+license and I have the right under that license to submit that
+work with modifications, whether created in whole or in part
+by me, under the same open source license (unless I am
+permitted to submit under a different license), as indicated
+in the file; or
+
+(c) The contribution was provided directly to me by some other
+person who certified (a), (b) or (c) and I have not modified
+it.
+
+(d) I understand and agree that this project and the contribution
+are public and that a record of the contribution (including all
+personal information I submit with it, including my sign-off) is
+maintained indefinitely and may be redistributed consistent with
+this project or the open source license(s) involved.
+```