Use relative links in markdown files

Our repository is sometimes copied into other repositories, at which
point all the absolute links don't work. README.md used "./whatever",
which seems to work most consistently, so copy that.

Change-Id: I63bbf01b8f3870112d1df571adaa6cc82f58e5eb
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/64347
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Hubert Chao <hchao@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/INCORPORATING.md b/INCORPORATING.md
index 96c6435..afe61d9 100644
--- a/INCORPORATING.md
+++ b/INCORPORATING.md
@@ -1,7 +1,7 @@
 # Incorporating BoringSSL into a project
 
 **Note**: if your target project is not a Google project then first read the
-[main README](/README.md) about the purpose of BoringSSL.
+[main README](./README.md) about the purpose of BoringSSL.
 
 If you are porting BoringSSL to a new platform see
 ["go/boringssl-on-new-platform"](https://goto.corp.google.com/boringssl-on-new-platform) (Google
@@ -68,7 +68,7 @@
 checked into the incorporating project's source repository. This avoids
 incorporating projects needing to support Perl and Go in their build systems.
 
-The script [`util/generate_build_files.py`](/util/generate_build_files.py)
+The script [`util/generate_build_files.py`](./util/generate_build_files.py)
 expects to be run from the `third_party/boringssl` directory and to find the
 BoringSSL source code in `src/`. You should pass it a single argument: the name
 of the build system that you're using. If you don't use any of the supported
@@ -76,7 +76,7 @@
 for it.
 
 The script will pregenerate the intermediate files (see
-[BUILDING.md](/BUILDING.md) for details about which tools will need to be
+[BUILDING.md](./BUILDING.md) for details about which tools will need to be
 installed) and output helper files for that build system. It doesn't generate a
 complete build script, just file and test lists, which change often. For
 example, see the