Add definition of pyenv help in COMMANDS.md (#2139)

COMMANDS.md

@@ -5,6 +5,7 @@ first argument.
 
 The most common subcommands are:
 
+* [`pyenv help`](#pyenv-help)
 * [`pyenv commands`](#pyenv-commands)
 * [`pyenv local`](#pyenv-local)
 * [`pyenv global`](#pyenv-global)
@@ -24,6 +25,11 @@ The most common subcommands are:
 * [`pyenv init`](#pyenv-init)
 * [`pyenv completions`](#pyenv-completions)
 
+## `pyenv help`
+
+List all available pyenv commands along with a brief description of what they do. Run `pyenv help <command>` for information on a specific command. For full documentation, see: https://github.com/pyenv/pyenv#readme
+
+
 ## `pyenv commands`
 
 Lists all available pyenv commands.
@@ -287,18 +293,18 @@ Lists all Python versions with the given command installed.
 
 ## `pyenv exec`
 
-    `Usage: pyenv exec <command> [arg1 arg2...]`
+    Usage: pyenv exec <command> [arg1 arg2...]
 
 Runs an executable by first preparing PATH so that the selected Python
 version's `bin` directory is at the front.
 
 For example, if the currently selected Python version is 3.9.7:
 
-    `pyenv exec pip install -r requirements.txt`
+    pyenv exec pip install -r requirements.txt
     
 is equivalent to:
 
-    `PATH="$PYENV_ROOT/versions/3.9.7/bin:$PATH" pip install -r requirements.txt`
+    PATH="$PYENV_ROOT/versions/3.9.7/bin:$PATH" pip install -r requirements.txt
 
 ## `pyenv root`