DOCs: update index and TOC to better organize how-to docs (#78)

docs/how-to/configuring-runtime-options.rst

@@ -43,6 +43,17 @@ and tweak the default sampling values.
    ROCPROFSYS_SAMPLING_CPUS        = all
    ROCPROFSYS_SAMPLING_GPUS        = $env:HIP_VISIBLE_DEVICES
 
+Use the configuration file
+-----------------------------------
+
+Tell rocprof-systems to use the modified settings by creating the environment variable ``ROCPROFSYS_CONFIG_FILE``
+
+.. code-block:: shell
+
+   export ROCPROFSYS_CONFIG_FILE=~/.rocprof-sys.cfg
+
+See :ref:`creating a configuration file<creating-a-configuration-file>` for more details.
+
 Exploring runtime settings
 -----------------------------------
 
@@ -1191,6 +1202,8 @@ Viewing hardware counters
    | LDSBankConflict:device=0              | The percentage of GPUTime LDS is s... |
    |---------------------------------------|---------------------------------------|
 
+.. _creating-a-configuration-file:
+
 Creating a configuration file
 ========================================