Added tuned profile for Nebula Graph (vesoft-inc#940)

* Added tuned profile for Nebula Graph

* add comment on min_free_kbytes

Co-authored-by: Sophie <84560950+Sophie-Xie@users.noreply.github.com>

Co-authored-by: dutor <440396+dutor@users.noreply.github.com>
Co-authored-by: Sophie <84560950+Sophie-Xie@users.noreply.github.com>

conf/tuned/README.md

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+# Summary
+
+These are tuned profile to configure the system to optimize for the Nebula Graph service.
+
+Follow below steps to utilize:
+ * Install the tuned service if absent, and enable it with `systemctl`.
+ * Copy the __nebula__ directory into `/etc/tuned`.
+ * Execute `tuned-adm profile nebula` to activate the profile.

conf/tuned/nebula/tuned.conf

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+[main]
+summary=Optimize for Nebula Graph DBMS
+include=latency-performance
+
+
+[vm]
+transparent_hugepages=never
+
+
+[sysctl]
+kernel.core_pattern=core
+kernel.core_uses_pid=1
+kernel.numa_balancing=0
+
+vm.swappiness=0
+vm.oom_dump_tasks=1
+# min_free_kbytes is suggested to set to approximately 2% of the total memory.
+# 1GB at least and 5GB at most.
+vm.min_free_kbytes=5242880
+vm.max_map_count=131060
+vm.dirty_background_ratio = 3
+vm.dirty_ratio = 20
+vm.dirty_expire_centisecs = 500
+vm.dirty_writeback_centisecs = 100
+
+net.core.busy_read=50
+net.core.busy_poll=50
+net.core.somaxconn=4096
+net.ipv4.tcp_max_syn_backlog=4096
+net.core.netdev_max_backlog=10240
+net.ipv4.tcp_fastopen=3
+net.ipv4.tcp_slow_start_after_idle=0