move to a simpler versioning policy for the Compiler.jl stdlib (#57520)

This commit adjusts /Compiler/Project.toml and adds a new
/Compiler/README.md based on the new versioning policy for the
Compiler.jl stdlib.

Regarding the new versioning policy and the latest way to use the
Compiler.jl stdlib, please refer to this comment[^1] and the newly added
READMEs (`JuliaLang/julia/Compiler/README.md`[^2] and 
and `JuliaLang/BaseCompiler.jl/README.md`[^3]).

[^1]: #57520 (comment)
[^2]: https://github.com/JuliaLang/julia/blob/a8f3e4d0603692ac79700890d3e8d35e904e000e/Compiler/README.md
[^3]: https://github.com/JuliaLang/BaseCompiler.jl

Author: aviatesk

Compiler/Project.toml

@@ -1,6 +1,6 @@
 name = "Compiler"
 uuid = "807dbc54-b67e-4c79-8afb-eafe4df6f2e1"
-version = "0.0.3"
+version = "0.0.0"
 
 [compat]
 julia = "1.10"

Compiler/README.md

@@ -0,0 +1,45 @@
+# The `Compiler` module
+
+This directory maintains the implementation of the Julia compiler.
+
+Through a bootstrapping process, it is bundled into the Julia runtime as `Base.Compiler`.
+
+You can also use this `Compiler` module as the `Compiler` standard library by following the steps below.
+
+## How to use
+
+To utilize this `Compiler.jl` standard library, you need to declare it as a dependency in
+your `Project.toml` as follows:
+> Project.toml
+```toml
+[deps]
+Compiler = "807dbc54-b67e-4c79-8afb-eafe4df6f2e1"
+
+[compat]
+Compiler = "0"
+```
+
+With the setup above, [the special placeholder version (v0.0.0)](https://github.com/JuliaLang/BaseCompiler.jl)
+will be installed by default.[^1]
+
+[^1]: Currently, only version v0.0.0 is registered in the [General](https://github.com/JuliaRegistries/General) registry.
+
+If needed, you can switch to a custom implementation of the `Compiler` module by running
+```julia-repl
+pkg> dev /path/to/Compiler.jl # to use a local implementation
+```
+or
+```julia-repl
+pkg> add https://url/of/Compiler/branch # to use a remote implementation
+```
+This feature is particularly useful for developing or experimenting with alternative compiler implementations.
+
+> [!note]
+> The Compiler.jl standard library is available starting from Julia v1.10.
+> However, switching to a custom compiler implementation is supported only from
+> Julia v1.12 onwards.
+
+> [!warning]
+> When using a custom, non-`Base` version of `Compiler` implementation, it may be necessary
+> to run `InteractiveUtils.@activate Compiler` to ensure proper functionality of certain
+> reflection utilities.