Add description

README.md

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-[![Build status](https://ci.appveyor.com/api/projects/status/l3s9xjgjx90fpdeh?svg=true)](https://ci.appveyor.com/project/MattOlenik/nativeinjector)
+[![Build status](https://ci.appveyor.com/api/projects/status/l3s9xjgjx90fpdeh?svg=true)](https://ci.appveyor.com/project/MattOlenik/nativeinjector)
+
+# About
+
+A simple .NET library for injecting native([PE](https://en.wikipedia.org/wiki/Portable_Executable)) DLLs into other processes from managed processes. It uses named shared memory to make a `byte[]` payload available to the remote process. It works by running LoadLibrary in the target process, resulting in `dllmain()` in your DLL being called, where your injected code will be. There are [important restrictions and best practices](https://msdn.microsoft.com/en-us/library/windows/desktop/dn633971.aspx#general_best_practices) regarding code that runs in dllmain(), so caution is advised. Doubly so because you're running code in a foreign process you know nothing about.
+
+It was written for simple, short-lived functions, such as the PATH injection used in [Winston](https://github.com/mattolenik/winston).
+
+# Example
+
+```csharp
+byte[] payload = Encoding.Unicode.GetBytes("some argument, struct, or other data");
+// Synchronously waits for dllmain() to finish, then unloads the DLL
+Injector.Inject(pid, dll32path, dll64path, "my shared memory name", payload);
+```
+
+## Mechanism
+
+1. Copy the payload to shared memory
+2. [Allocate memory](https://msdn.microsoft.com/en-us/library/windows/desktop/aa366890.aspx) in the target process
+3. Copy the path of the DLL to be injected into previously allocated memory
+4. [Create a remote thread](https://msdn.microsoft.com/en-us/library/windows/desktop/ms682437.aspx) to execute LoadLibrary, passing a pointer to the above memory for its argument
+5. LoadLibrary calls the DLL's dllmain(), where your injected code runs
+6. Injector waits for code to finish then unloads the DLL
+
+