Document Alpine Linux build quirk in BUILD.md

On Alpine Linux and other musl-based distributions, the
`x86_64-unknown-linux-musl` Rust target statically links musl by
default. When the binary dynamically links to Alpine's OpenSSL (which
itself links to Alpine's musl), two different musl instances exist in
the same process, causing segmentation faults at runtime.

This change adds `BUILD.md` documenting the issue and the solution:
setting `RUSTFLAGS="-C target-feature=-crt-static"` to dynamically link
musl. The document includes the root cause explanation, the fix, and
references to the original discussions.

Author: lukebakken

BUILD.md

@@ -0,0 +1,32 @@
+# Building rabbitmqadmin
+
+## Standard Build
+
+```bash
+cargo build --release
+```
+
+## Alpine Linux / musl-based Systems
+
+When building on Alpine Linux or other musl-based distributions, you must configure Rust to dynamically link against the system's musl libc to avoid segmentation faults.
+
+### The Problem
+
+The `x86_64-unknown-linux-musl` target statically links musl by default. When your binary dynamically links to Alpine's OpenSSL (which itself links to Alpine's musl), you end up with two different musl instances in the same process, causing segmentation faults at runtime.
+
+### The Solution
+
+Set the `RUSTFLAGS` environment variable to dynamically link musl:
+
+```bash
+RUSTFLAGS="-C target-feature=-crt-static" cargo build --release
+```
+
+### Alternative: Static Linking
+
+Alternatively, you can statically link OpenSSL by enabling the `vendored` feature in dependencies that use OpenSSL. However, this approach is not currently configured in this project.
+
+### References
+
+- [Rust Users Forum: SIGSEGV with program linked against OpenSSL in an Alpine container](https://users.rust-lang.org/t/sigsegv-with-program-linked-against-openssl-in-an-alpine-container/52172)
+- [GitHub Discussion #99](https://github.com/rabbitmq/rabbitmqadmin-ng/discussions/99)