meson: Add subprojects file

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Id3421e45d2f5f329a7d27d5c6324ceb528a46383
diff --git a/subprojects/nlohmann-json.wrap b/subprojects/nlohmann-json.wrap
new file mode 100644
index 0000000..a2884b1
--- /dev/null
+++ b/subprojects/nlohmann-json.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+url = https://github.com/nlohmann/json
+revision = HEAD
+
+[provide]
+nlohmann-json = nlohmann_json_dep