regulators: Update inventory paths in docs/example

Updated the JSON configuration file documentation and example to clarify
that inventory paths are relative.

JSON configuration file documentation changes:
* Described how inventory paths are relative to the root
  /xyz/openbmc_project/inventory.
* Removed leading slashes from the example inventory paths.

Example JSON configuration file changes:
* Remove leading slashes from the inventory paths.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: Iec602f76e663c120b40017f3d12fb526b93c0ce5
diff --git a/phosphor-regulators/examples/config_file.json b/phosphor-regulators/examples/config_file.json
index 701322d..f18237e 100644
--- a/phosphor-regulators/examples/config_file.json
+++ b/phosphor-regulators/examples/config_file.json
@@ -57,7 +57,7 @@
           "comments": [ "IR35221 regulator producing the Vdd rail" ],
           "id": "vdd_regulator",
           "is_regulator": true,
-          "fru": "/system/chassis/motherboard/regulator1",
+          "fru": "system/chassis/motherboard/regulator1",
           "i2c_interface": {
             "bus": 1,
             "address": "0x70"
@@ -81,7 +81,7 @@
           "comments": [ "IR35221 regulator producing the Vio rail" ],
           "id": "vio_regulator",
           "is_regulator": true,
-          "fru": "/system/chassis/motherboard/regulator2",
+          "fru": "system/chassis/motherboard/regulator2",
           "i2c_interface": {
             "bus": 1,
             "address": "0x71"