Improve documentation of the force_max_q option

Document the values (including the default value) of force_max_q. Make
it clear force_max_q is a boolean flag rather than sets the value of the
max q.

Change-Id: Id5e1040b6357908ddb400c654d911509e4906a3b
(cherry picked from commit 7798826675b9f090ac1fa23572d3e5b85ef48a8a)

av1/arg_defs.c

diff --git a/av1/arg_defs.c b/av1/arg_defs.c
index a3eefc9..9a3352c 100644
--- a/av1/arg_defs.c
+++ b/av1/arg_defs.c
@@ -727,7 +727,8 @@
               "Check that input samples are within the valid range "
               "for the chosen bit depth with high bit depth encoding (0: "
               "disabled, 1: enabled (default))"),
-  .force_max_q =
-      ARG_DEF(NULL, "force-max-q", 1, "Force max Q used in vbr mode."),
+  .force_max_q = ARG_DEF(
+      NULL, "force-max-q", 1,
+      "Force the use of max Q in VBR mode (0: false (default), 1: true)."),
 #endif  // CONFIG_AV1_ENCODER
 };

av1/encoder/encoder.h

diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index b15f0ff..82e9cab 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -621,7 +621,7 @@
    */
   int max_consec_drop_ms;
   /*!
-   * Force to allow the usage of maximum q in vbr mode.
+   * Force the use of maximum q in vbr mode.
    */
   int force_max_q;
 } RateControlCfg;