add memory hint to ninja build intruction

web/content/docs/devguide/getting-started/build.md

@@ -38,6 +38,8 @@ To build with the `ninja` tool on the shell go to your previously configured bui
 cd ../build/release
 ninja
 ```
+By default, `ninja` uses maximum parallelism causing it to crash on many machines as the memory consumption exceeds the available memory.
+Therefore, we recommend restricting the number of threads to be used, e.g., type `ninja -j 2` for a maximum of two threads.
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