add public domain licensing example, fix typos (#189)

* Update clause_7_normative_text.adoc

* Update PER_data_policy.adoc

* Update PER_data_policy.adoc

* Update clause_7_normative_text.adoc

* Update clause_7_normative_text.adoc

standard/recommendations/core/PER_data_policy.adoc

@@ -3,7 +3,7 @@
 |===
 ^|*Permission {counter:per-id}* |*/per/core/data_policy*
 ^|A|For core data (when `+properties.wmo:dataPolicy+` property is `+core+`), attribution licensing MAY be provided as needed.
-^|B|For core data (when `+properties.wmo:dataPolicy+` is `+core+`) or recommended data (when `+properties.wmo:dataPolicy+` is `+recommended+`, and the data is compatible with feee and unrestricted principles), a license or public domain statement that is compatible with free and unrestricted principles (e.g., Creative Commons CC0footnote:[https://creativecommons.org/public-domain/cc0] or CC-BY 4.0footnote:[https://creativecommons.org/licenses/by/4.0]) MAY be expressed as a link object with the `license` link relation.
+^|B|For core data (when `+properties.wmo:dataPolicy+` is `+core+`) or recommended data (when `+properties.wmo:dataPolicy+` is `+recommended+`, and the data is compatible with free and unrestricted principles), a license or public domain statement that is compatible with free and unrestricted principles (e.g., Creative Commons CC0footnote:[https://creativecommons.org/publicdomain/zero/1.0/]) MAY be expressed as a link object with the `license` link relation.
 ^|C|For core data (when `+properties.wmo:dataPolicy+` is `+core+`) or recommended data (when `+properties.wmo:dataPolicy+` is `+recommended+`, a copyright statement MAY be expressed in `+properties.rights+`
 ^|D|For core data (when `+properties.wmo:dataPolicy+` is `+core+`) or recommended data (when `+properties.wmo:dataPolicy+` is `+recommended+`, a link object MAY be expressed with `+rel=copyright+`.
 |===

standard/sections/clause_7_normative_text.adoc

@@ -574,7 +574,7 @@ A contact can also be specified by using a URL.
   "contacts": [{
     "organization": "Government of Canada; Environment and Climate Change Canada; Meteorological Service of Canada",
     "links": [{
-      "href": "https://exmaple.org/about",
+      "href": "https://example.org/about",
       "rel": "about",
       "type": "text/html"
     }],
@@ -747,6 +747,22 @@ It is useful to add provider-specific details to have the most detailed informat
 }]
 ----
 
+.Example: License for recommended data in the public domain
+[source,json]
+----
+"properties": {
+  ...
+  "wmo:dataPolicy": "recommended"
+  ...
+},
+"links": [{
+  "rel": "license",
+  "href": "https://creativecommons.org/publicdomain/zero/1.0/",
+  "type": "text/html",
+  "title": "CC0 1.0 Deed | CC0 1.0 Universal | Creative Commons"
+}]
+----
+
 To express rights not address by a license, the `+rights+` property can be used as follows:
 
 .Example: Rights