Add summary table

Signed-off-by: Philippe Ombredanne <pombredanne@aboutcode.org>

Author: pombredanne

docs/standard/summary.md

@@ -25,6 +25,19 @@ The definition for each components is:
   Optional.
 
 
+Table 1: Components of a PURL
+
+| Component  | Requirement | Description|
+| ---------- | ----------- |:------------------------------------------------------ |
+| scheme     | Required    | The URL scheme with the constant value of "pkg". One of the primary reasons for this single scheme is to facilitate the future official registration of the "pkg" scheme for package URLs. |
+| type       | Required    | The package "type" or package "protocol" such as maven, npm, nuget, gem, pypi, etc. |
+| namespace  | Optional    | A name prefix such as a Maven groupid, a Docker image owner, a GitHub user or organization. Namespace is type-specific. |
+| name       | Required    | The name of the package. |
+| version    | Optional    | The version of the package.  |
+| qualifiers | Optional    | Qualifier data for a package such as OS, architecture, repository, etc. Qualifiers are type-specific. |
+| subpath    | Optional    | Subpath within a package, relative to the package root. |
+
+
 Components are designed such that they form a hierarchy from the most significant
 on the left to the least significant components on the right.