Added readme file

Author: lukaskabrt

readme.md

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+# PoExtractor
+
+This utility extracts translatable strings from the C# code and from the Razor templates to POT (portable object template) files. It is designed to follow conventions used in the OrchardCore project.
+
+## Usage
+
+`PoExtractor.exe inputpath outputpath`
+
+Extracts all translatable strings from the projects at specified input path and saves generated POT files at the specified output path. It creates one POT file per a project.
+
+## Limitations
+
+PoExtractor assumes, the code follows several conventions
+
+* `IStringLocalizer` or a derived class is accessed via property named `T`
+* context of the localizable string is full name (with namespace) of the containing class for C# code
+* context of the localizable string is dot-delimited relative path to view for Razor templates
+
+## Example
+
+C# code:
+```csharp
+namespace OrchardCore.ContentFields.Fields { 
+    public class LinkFieldDisplayDriver : ContentFieldDisplayDriver<LinkField> {
+        public LinkFieldDisplayDriver(IStringLocalizer<LinkFieldDisplayDriver> localizer) {
+            T = localizer;
+        }
+
+        public IStringLocalizer T { get; set; }
+        
+        public override async Task<IDisplayResult> UpdateAsync(LinkField field, IUpdateModel updater, UpdateFieldEditorContext context) {
+            bool modelUpdated = await updater.TryUpdateModelAsync(field, Prefix, f => f.Url, f => f.Text);
+
+            if (modelUpdated)
+            {
+                var settings = context.PartFieldDefinition.Settings.ToObject<LinkFieldSettings>();
+
+                if (settings.Required && String.IsNullOrWhiteSpace(field.Url))
+                {
+                    updater.ModelState.AddModelError(Prefix, T["The url is required for {0}.", context.PartFieldDefinition.DisplayName()]);
+                }
+            }
+
+            return Edit(field, context);
+        }
+    }
+}
+```
+
+Razor view:
+```html
+@model OrchardCore.ContentFields.ViewModels.EditLinkFieldViewModel
+
+<div class="row">
+    <fieldset class="form-group col-md-12">
+        <label asp-for="Url">@Model.PartFieldDefinition.DisplayName()</label>
+    </fieldset>
+    <fieldset class="form-group col-md-6" asp-validation-class-for="Url">
+        <input asp-for="Url" class="form-control content-preview-text" placeholder="@settings.UrlPlaceholder" required="@isRequired" />
+    </fieldset>
+    <fieldset class="form-group col-md-6" asp-validation-class-for="Text">
+        <label asp-for="Text" @if (settings.LinkTextMode == LinkTextMode.Required) { <text> class="required" </text>  }>@T["Link text"]</label>
+        <input asp-for="Text" type="text" class="form-control content-preview-text" placeholder="@settings.TextPlaceholder" required="@isTextRequired" />
+    </fieldset>
+</div>
+
+```
+
+Generated POT file:
+```
+#: OrchardCore.ContentFields\Drivers\LinkFieldDriver.cs:59
+#. updater.ModelState.AddModelError(Prefix, T["The url is required for {0}.", context.PartFieldDefinition.DisplayName()]);
+msgctxt "OrchardCore.ContentFields.Fields.LinkFieldDisplayDriver"
+msgid "The url is required for {0}."
+msgstr ""
+
+#: OrchardCore.ContentFields\Views\LinkField.Edit.cshtml:32
+#. <label asp-for="Text" @if (settings.LinkTextMode == LinkTextMode.Required) { <text> class="required" </text>  }>@T["Link text"]</label>
+msgctxt "OrchardCore.ContentFields.Views.LinkField.Edit"
+msgid "Link text"
+msgstr ""
+```