docs: document benchmark_min_time CLI forms (#2154)

* docs: document benchmark_min_time CLI forms

* chore: trigger CLA rescan

* docs: clarify benchmark_min_time precedence

AUTHORS

diff --git a/AUTHORS b/AUTHORS
index f3f29d6..bea19b3 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -32,6 +32,7 @@
 Fabien Pichot <pichot.fabien@gmail.com>
 Federico Ficarelli <federico.ficarelli@gmail.com>
 Felix Homann <linuxaudio@showlabor.de>
+Felmon Fekadu <felmonon@gmail.com>
 Gergely Meszaros <maetveis@gmail.com>
 Gergő Szitár <szitar.gergo@gmail.com>
 Google Inc.

CONTRIBUTORS

diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index a88240c..c3f6789 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -52,6 +52,7 @@
 Fanbo Meng <fanbo.meng@ibm.com>
 Federico Ficarelli <federico.ficarelli@gmail.com>
 Felix Homann <linuxaudio@showlabor.de>
+Felmon Fekadu <felmonon@gmail.com>
 Geoffrey Martin-Noble <gcmn@google.com> <gmngeoffrey@gmail.com>
 Gergely Meszaros <maetveis@gmail.com>
 Gergő Szitár <szitar.gergo@gmail.com>

docs/user_guide.md

diff --git a/docs/user_guide.md b/docs/user_guide.md
index b2e6975..c09d775 100644
--- a/docs/user_guide.md
+++ b/docs/user_guide.md
@@ -252,6 +252,32 @@
 the minimum time, or the wallclock time is 5x minimum time. The minimum time is
 set per benchmark by calling `MinTime` on the registered benchmark object.
 
+The minimum time can also be set for all benchmarks with the
+`--benchmark_min_time=<value>` command-line option. This flag supports two
+forms:
+
+* `--benchmark_min_time=<float>s` sets the minimum running time for each
+  benchmark repetition in seconds.
+* `--benchmark_min_time=<integer>x` runs each benchmark repetition for an
+  explicit number of iterations instead of using the dynamic time-based
+  iteration selection. This applies to benchmarks that do not already specify
+  an explicit iteration count in code.
+
+For compatibility, bare numeric values such as `--benchmark_min_time=0.5` are
+also interpreted as seconds, but the explicit `s` suffix is preferred for
+clarity.
+
+For example:
+
+```bash
+$ ./run_benchmarks.x --benchmark_min_time=0.5s
+$ ./run_benchmarks.x --benchmark_min_time=100x
+```
+
+If a benchmark specifies its own `MinTime()` or `Iterations()` in code, those
+per-benchmark settings take precedence over the corresponding
+`--benchmark_min_time` command-line forms.
+
 Furthermore warming up a benchmark might be necessary in order to get
 stable results because of e.g caching effects of the code under benchmark.
 Warming up means running the benchmark a given amount of time, before