Checkpatch.pl should probably exclude *.rst files from the SPDX License
Identifier check, since they are documentational files, like *.txt. 
Here is the warning message I got on a recent documentation patch I
created.

WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
#28: FILE: Documentation/networking/fm10k.rst:1:
+Linux* Base Driver for Intel(R) Ethernet Multi-host Controller

total: 0 errors, 1 warnings, 0 checks, 162 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-
inplace.

.apply/v4-Documentation-fm10k-Add-kernel-documentation.patch has style
problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.