Profile: Improve module docstring (#52678)

![Screenshot 2023-12-30 at 7 24
10 PM](https://github.com/JuliaLang/julia/assets/1694067/a7c78943-5e4a-475c-864c-3b0005305471)

(cherry picked from commit 0f62824)

stdlib/Profile/src/Profile.jl

@@ -1,7 +1,24 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
 """
-Profiling support, main entry point is the [`@profile`](@ref) macro.
+    Profile
+
+Profiling support.
+
+## CPU profiling
+- `@profile foo()` to profile a specific call.
+- `Profile.print()` to print the report.
+- `Profile.clear()` to clear the buffer.
+- Send a $(Sys.isbsd() ? "SIGINFO (ctrl-t)" : "SIGUSR1") signal to the process to automatically trigger a profile and print.
+
+## Memory profiling
+- `Profile.Allocs.@profile [sample_rate=0.1] foo()` to sample allocations within a specific call. A sample rate of 1.0 will record everything; 0.0 will record nothing.
+- `Profile.Allocs.print()` to print the report.
+- `Profile.Allocs.clear()` to clear the buffer.
+
+## Heap profiling
+- `Profile.take_heap_snapshot()` to record a `.heapsnapshot` record of the heap.
+- Set `JULIA_PROFILE_PEEK_HEAP_SNAPSHOT=true` to capture a heap snapshot when signal $(Sys.isbsd() ? "SIGINFO (ctrl-t)" : "SIGUSR1") is sent.
 """
 module Profile