avoid shipping junk files

I did a diff of the shipped file list with master branch and it looks
good after this commit.

1 files changed, 1 insertions, 1 deletions

diff --git a/build.zig b/build.zig
index d6e365b02d..2cd0804894 100644
--- a/build.zig
+++ b/build.zig
@@ -91,7 +91,7 @@ pub fn build(b: *Builder) !void {
         .source_dir = "std",
         .install_dir = .Lib,
         .install_subdir = "zig" ++ fs.path.sep_str ++ "std",
-        .exclude_extensions = [_][]const u8{"test.zig"},
+        .exclude_extensions = [_][]const u8{ "test.zig", "README.md" },
     });
 
     const test_filter = b.option([]const u8, "test-filter", "Skip tests that do not match filter");