README: add usage and benchmark

Author: zchee

README.md

@@ -1,3 +1,42 @@
 # kube-tmux
 
 Command kube-tmux prints Kubernetes context and namespace to tmux status line.
+
+## Usage
+
+```console
+$ kube-tmux -h
+Usage of kube-tmux:
+  -ctxBg string
+        Context background colour
+  -ctxFg string
+        Context foreground colour
+  -nsBg string
+        Nasespace background colour
+  -nsFg string
+        Nasespace foreground colour
+  -sepBg string
+        Separator background colour
+  -sepFg string
+        Separator foreground colour
+  -separator string
+        Separator of Context and Nasespace (default "/")
+```
+
+```console
+set -g status-right "#(kube-tmux -separator=':' -ctxFg='colour011#,bright' -ctxBg 'default' -sepFg 'colour015#,bright' -nsFg 'colour075#,bright')"
+```
+
+## Benchmark
+
+```console
+$ hyperfine -S /usr/local/bin/bash --max-runs 10 --warmup 3 'kube.tmux'
+Benchmark #1: kube.tmux
+  Time (mean ± σ):     109.0 ms ±   2.7 ms    [User: 102.7 ms, System: 37.0 ms]
+  Range (min … max):   106.8 ms … 116.3 ms    10 runs
+
+$ hyperfine -S /usr/local/bin/bash --max-runs 10 --warmup 3 "kube-tmux -separator=':' -ctxFg='colour011#,bright' -ctxBg 'default' -sepFg 'colour015#,bright' -nsFg 'colour075#,bright'"
+Benchmark #1: kube-tmux -separator=':' -ctxFg='colour011#,bright' -ctxBg 'default' -sepFg 'colour015#,bright' -nsFg 'colour075#,bright'
+  Time (mean ± σ):      10.8 ms ±   0.6 ms    [User: 6.7 ms, System: 2.7 ms]
+  Range (min … max):    10.3 ms …  12.1 ms    10 runs
+```