Properly link flecs library

engine/libs/flecs/examples/build/bazel/README.md

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+You can include the flecs repository in your `WORKSPACE` with:
+
+```bazel
+git_repository(
+    name = "flecs",
+    remote = "https://github.com/SanderMertens/flecs",
+    commit = "f150d96ba9ea8be2b24dbf2217368c231cb17720", # v2.3.2+merge329
+    shallow_since = "1615075784 -0800",
+)
+```
+
+And then add it to your `BUILD` with:
+
+```bazel
+    deps = ["@flecs//:flecs"]
+```
+
+This directory contains a complete example of this usage. To try it you can run the following from your terminal:
+
+```
+bazel run example
+```