Add `Edit on GitHub`

resolved #115

The following configuration need to be added to [config.yml](https://github.com/go-gitea/gitea/blob/main/docs/config.yaml)

```yml
params:
  github_doc_repository: "https://github.com/go-gitea/gitea"
  github_doc_repository_path: "docs/content"
```

Signed-off-by: Xinyu Zhou <i@sourcehut.net>

i18n/en-US.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Next"
+
+- id: edit_on_github
+  translation: "Edit on GitHub"

i18n/nl-NL.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Volgende"
+
+- id: edit_on_github
+  translation: "Bewerken op GitHub"

i18n/pt-BR.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Próximo"
+
+- id: edit_on_github
+  translation: "Edite em GitHub"

i18n/zh-CN.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "后一页"
+
+- id: edit_on_github
+  translation: "在 GitHub 上编辑此页面"

i18n/zh-TW.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "下一頁"
+
+- id: edit_on_github
+  translation: "在 GitHub 上編輯此頁面"

layouts/doc/single.html

@@ -10,6 +10,8 @@
 			<div class="column is-three-quarters">
 				<div class="content">
 					{{ .Content }}
+					<hr>
+					{{ partial "edit-this" . }}
 				</div>
 			</div>
 		</div>

layouts/page/single.html

@@ -10,6 +10,8 @@
 			<div class="column">
 				<div class=" content">
 					{{ .Content }}
+					<hr>
+					{{ partial "edit-this" . }}
 				</div>
 			</div>
 		</div>

layouts/partials/edit-this.html

@@ -0,0 +1,3 @@
+{{- if and .Site.Params.github_doc_repository .File -}}
+<a href="{{ .Site.Params.github_doc_repository }}/edit/main/{{ .Site.Params.github_doc_repository_path }}/{{ .File.Path }}" class="edit-page"><i class="fas fa-pen-square"></i>{{- T "edit_on_github" -}}</a>
+{{- end -}}