Ports: Add ReadMe files explaining port patches that have explanations

Ports/mold/patches/ReadMe.md

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+# Patches for mold on SerenityOS
+
+## `0001-Disable-mold_preload.so-for-Serenity.patch`
+This feature depends on RTLD_NEXT capabilities which are not yet
+implemented in the Serenity DynamicLoader.
+
+## `0002-Disable-mimalloc-for-serenity.patch`
+mimalloc needs some help to compile on serenity. That's one yak too
+far for right now.
+
+## `0004-Add-POSIX-headers-for-timeval-and-select.patch`
+mold was relying on other libc implementations leaking these definitions
+from other headers.
+
+## `0005-Tell-TBB-that-SerenityOS-does-not-support-weak-symbo.patch`
+Something about the Clang toolchain configuration causes undefined weak
+references to scalable_malloc to remain in the mold executable even
+though there's no chance we'll be loading the tbbmalloc library at
+runtime. So, just lie to TBB that we don't support weak symbols.
+
+## `0006-Tell-TBB-that-SerenityOS-libraries-are-named-like-BS.patch`
+We won't be loading these libraries when building TBB as a static
+library for mold, but the OS detection logic still needs updated.
+
+## `0007-Stub-out-a-definition-of-RTLD_NOLOAD.patch`
+SerenityOS's DynamicLoader doesn't support this flag. However, we won't
+be dynamically loading any tbb extensions for the static library build
+mold uses, so we can just define it as a no-op as the code paths that
+use it will never be used.