Microsoft.Extensions.StaticAnalysis Readme (#4594)

* Fill in the readme

* -ruleset

src/Packages/Microsoft.Extensions.StaticAnalysis/Microsoft.Extensions.StaticAnalysis.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <PackageId>Microsoft.Extensions.StaticAnalysis</PackageId>
-    <Description>Curated set of code analyzers and code analyzer settings.</Description>
+    <Description>A curated set of code analyzers and code analyzer settings.</Description>
     <Workstream>Fundamentals</Workstream>
     <Category>Static Analysis</Category>
   </PropertyGroup>

src/Packages/Microsoft.Extensions.StaticAnalysis/README.md

@@ -1 +1,52 @@
-README
+# Microsoft.Extensions.StaticAnalysis
+
+A curated set of code analyzers and code analyzer settings.
+
+## Install the package
+
+From the command-line:
+
+```dotnetcli
+dotnet add package Microsoft.Extensions.StaticAnalysis
+```
+
+Or directly in the C# project file:
+
+```xml
+<ItemGroup>
+  <PackageReference Include="Microsoft.Extensions.StaticAnalysis" Version="[CURRENTVERSION]" >
+    <PrivateAssets>all</PrivateAssets>
+    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+  </PackageReference>
+</ItemGroup>
+```
+
+## Usage Example
+
+On install, a warning will be displayed that `The StaticAnalysisCodeType property is not defined, assuming 'General'`. The General set of diagnostics is enabled by default. To select a different set of diagnostics (or hide the warning) add the `StaticAnalysisCodeType` property to your project as follows.
+
+```XML
+  <PropertyGroup>
+    <StaticAnalysisCodeType>General</StaticAnalysisCodeType>
+  </PropertyGroup>
+```
+
+## Available Sets Of Diagnostics
+
+Different pre-defined sets of diagnostics are available depending on the type of project being built. These can be specified in the StaticAnalysisCodeType property:
+- Benchmark: Projects used for benchmarking.
+- General: Any type of project.
+- NonProdExe: Projects that produce an exe for non-production use.
+- NonProdLib: Projects that produce a library (dll) for non-production use.
+- ProdExe: Projects that produce an exe for production use.
+- ProdLib: Projects that produce a library (dll) for production use.
+- Test: Projects used for testing.
+
+Each of these also has an optional `-Tier1` and a `-Tier2` variant (e.g. `General-Tier1`).
+- `Tier1` enables only the most important diagnostics from this set.
+- `Tier2` includes Tier1 diagnostics and others that aren't as critical.
+- The names without `Tier` suffixes include all diagnostics from tier's 1 and 2, and any others that are applicable.
+
+## Feedback & Contributing
+
+We welcome feedback and contributions in [our GitHub repo](https://github.com/dotnet/extensions).