Improving docs about test script creation (#560)

* Adding in information about test script creation in docs

* Update docs/manual.md

Updated suggestion

Co-Authored-By: Pedro Medeiros <13643195+pedroMMM@users.noreply.github.com>

* Update docs/manual.md

Updated suggestion

Co-Authored-By: Pedro Medeiros <13643195+pedroMMM@users.noreply.github.com>

* Update docs/manual.md

Updated suggestion

Co-Authored-By: Pedro Medeiros <13643195+pedroMMM@users.noreply.github.com>

* Update docs/manual.md

Updated suggestion.

Co-Authored-By: Pedro Medeiros <13643195+pedroMMM@users.noreply.github.com>

Co-authored-by: Pedro Medeiros <13643195+pedroMMM@users.noreply.github.com>

docs/manual.md

@@ -12,6 +12,7 @@
     * [render, r \- Render gossfile after importing all referenced gossfiles](#render-r---render-gossfile-after-importing-all-referenced-gossfiles)
     * [serve, s \- Serve a health endpoint](#serve-s---serve-a-health-endpoint)
     * [validate, v \- Validate the system](#validate-v---validate-the-system)
+* [Goss test creation](#goss-test-creation)
 * [Important note about goss file format](#important-note-about-goss-file-format)
 * [Available tests](#available-tests)
   * [addr](#addr)
@@ -322,6 +323,29 @@ $ echo $?
 2
 ```
 
+## Goss test creation
+Goss tests can be created by using either of following methods.
+1. goss autoadd <resource to test>
+2. goss add <resource to test> 
+3. manually create YAML/JSON test file by hand.
+
+To customize the parameters generated by `goss add` and `goss autoadd` YAML file you need to manually edit it.
+
+`goss add package nginx` will generate below YAML
+```
+package:
+  nginx:
+    installed: true
+    versions:
+    - 1.17.8
+```
+To test uninstall scenario you would need to manually edit it and set it as below.
+```
+package:
+  nginx:
+    installed: false
+```
+
 ## Important note about goss file format
 It is important to note that both YAML and JSON are formats that describe a nested data structure.