Add zstd finder file (#165)

Findzstd.cmake

@@ -0,0 +1,41 @@
+if (TARGET zstd::zstd)
+  return()
+endif()
+
+include(FindPackageHandleStandardArgs)
+
+if (APPLE)
+  file(GLOB ZSTD_DIRS
+    /usr/local/Cellar/zstd/*
+    /opt/homebrew/Cellar/zstd/*
+  )
+endif()
+
+find_path(zstd_INCLUDE_DIR
+  NAMES zstd.h
+  HINTS ${ZSTD_DIRS}
+  PATH_SUFFIXES include
+)
+
+find_library(zstd_LIBRARY
+  NAMES zstd
+  HINTS ${ZSTD_DIRS}
+  PATH_SUFFIXES lib
+)
+
+find_package_handle_standard_args(zstd REQUIRED_VARS
+    zstd_LIBRARY
+    zstd_INCLUDE_DIR
+)
+
+if (zstd_FOUND)
+  mark_as_advanced(zstd_LIBRARY)
+  mark_as_advanced(zstd_INCLUDE_DIR)
+
+  add_library(zstd::zstd UNKNOWN IMPORTED)
+  set_target_properties(zstd::zstd
+      PROPERTIES
+      IMPORTED_LOCATION ${zstd_LIBRARY}
+      INTERFACE_INCLUDE_DIRECTORIES ${zstd_INCLUDE_DIR}
+  )
+endif ()