Added some documentation

Author: drowaudio

README.md

@@ -1,6 +1,86 @@
 # rtcheck
 Dynamic library to catch run-time safety violations heavily inspired by [RADSan](https://github.com/realtime-sanitizer/radsan)
 
+## Contents
+- [Adding rtcheck to a project](#adding-rtcheck-to-a-project)
+- [Using rtcheck](#using-rtcheck)
+- [Disabling checks](#disabling-checks)
+- [Catching your own violations](#catching-your-own-violations)
+- [Error modes](#error-modes)
+
+## Adding rtcheck to a project
+
+## Using rtcheck
+Simply add an instance of rtc::realtime_context at the start of the scope you want to check for real-time safety violations like this:  
+```c++
+int main()
+{
+    std::thread t ([]
+    {
+        rtc::realtime_context rc;
+        malloc (1024); // Allocating memory is a real-time safety violation!
+    });
+
+    t.join();
+
+    return 0;
+}
+```
+The call to malloc in the above code will then be caught and logged as so:
+```
+Real-time violation: intercepted call to real-time unsafe function malloc in real-time context! Stack trace:
+0   librt_check.dylib                   0x000000010543f7d4 _ZN3rtc14get_stacktraceEv + 84
+ 1   librt_check.dylib                   0x000000010543f450 _ZN3rtc32log_function_if_realtime_contextEPKc + 300
+  2   librt_check.dylib                   0x000000010543fe00 _Z44log_function_if_realtime_context_and_enabledN3rtc11check_flagsEPKc + 64
+   3   librt_check.dylib                   0x000000010543fe30 wrap_malloc + 32
+    4   fail_malloc                         0x0000000104fcff14 main + 32
+     5   dyld                                0x00000001901760e0 start + 2360
+```
+
+## Disabling checks
+There are two ways to disable checks. You can either disable all checks, which can be useful if you 
+know you'll be calling a potentially unsafe function but in a safe way (e.g. an un-contented lock), or you want to log something:
+```c++
+{
+    rtc::non_realtime_context nrc;
+    std::cout << "need to get this message on the screen!";
+}
+```
+Or you can selectively disable checks:
+```c++
+{
+    rtc::disable_checks_for_thread (check_flags::threads);
+    mutex.lock(); // I know this is uncontended, don't for get to unlock!
+}
+```
+
+## Catching your own violations
+If you have some code which you know is non-real-time safe e.g. an unbounded distribution function or some other async call, you can opt-in to let rtcheck catch it by calling the following function:
+```c++
+void my_unsafe_function()
+{
+    log_function_if_realtime_context (__func__);
+}
+```
+This will then get logged if called whilst a `rtc::realtime_context` is alive.
+
+## Error Modes
+There are two currently supported error modes
+- Exit with error code 1 (default)
+- Log and continue
+
+Exiting it useful for CI runs where you want the program to terminate in an obvious way (non-zero exit code) to fail the run.
+In normal use though, you may just want to log the violation and continue.
+
+You can change between these globally using the following function:
+```c++
+/** Sets the global error more to determine the behaviour when a real-time
+    violation is detected.
+*/
+void set_error_mode (error_mode);
+```
+---
+# Notes:
 ## Features
 - [x] Enable in scope
 - [x] Disable in scope
@@ -78,7 +158,7 @@ Dynamic library to catch run-time safety violations heavily inspired by [RADSan]
 - Passes
   - [x] Atomic double
   - [x] Small std::function
-  - [ ] thread_local? (pass on linux, fail on macOS)
+  - [x] thread_local? (pass on linux, fail on macOS)
 - [x] Running on CI Linux
 - [x] Running on CI macOS
 - [x] Tests via CTest (can catch failues)