Add Edit on GitHub (#116)

resolved #115

The following configuration need to be added to [config.yml](https://github.com/go-gitea/gitea/blob/main/docs/config.yaml) ([go-gitea/gitea#21981](https://github.com/go-gitea/gitea/pull/21981))

```yml
params:
  repo: "https://github.com/go-gitea/gitea"
  docContentPath: "docs/content"
```

Signed-off-by: Xinyu Zhou <i@sourcehut.net>
Reviewed-on: https://gitea.com/gitea/theme/pulls/116
Reviewed-by: silverwind <silverwind@noreply.gitea.io>
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Xinyu Zhou <i@sourcehut.net>
Co-committed-by: Xinyu Zhou <i@sourcehut.net>

i18n/en-US.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Next"
+
+- id: edit_this_page
+  translation: "Edit this page"

i18n/nl-NL.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Volgende"
+
+- id: edit_this_page
+  translation: "Bewerk deze pagina"

i18n/pt-BR.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "Próximo"
+
+- id: edit_this_page
+  translation: "Edite essa página"

i18n/zh-CN.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "后一页"
+
+- id: edit_this_page
+  translation: "编辑此页面"

i18n/zh-TW.yaml

@@ -12,3 +12,6 @@
 
 - id: page_next
   translation: "下一頁"
+
+- id: edit_this_page
+  translation: "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_page" . }}
 				</div>
 			</div>
 		</div>

layouts/page/single.html

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

layouts/partials/edit-this-page.html

@@ -0,0 +1,3 @@
+{{- if and .Site.Params.repo .File -}}
+<a href="{{ .Site.Params.repo }}/edit/main/{{ .Site.Params.docContentPath }}/{{ .File.Path }}">{{- T "edit_this_page" -}}</a>
+{{- end -}}