Add document for -mstrict-align and -mno-strict-align

We have those two option for a while, but not document in this repo yet,
however we are intend to claify the scope of the option recently, so
it's time to document down what we have agree among different community.

README.mkd

@@ -400,11 +400,22 @@ specification, and in the draft [CORE-V Builtin
 Function](https://github.com/openhwgroup/core-v-sw/blob/master/specifications/corev-builtin-spec.md)
 specification.
 
+## Common Toolchain Command Line Options
+
+This section lists common RISC-V specific toolchain command line options.
+
+### `-mstrict-align`/`-mno-strict-align`
+Control the code generation for scalar memory access with strict alignment (also known as unaligned access or misaligned access).
+
+`-mstrict-align`: The compiler disallows misaligned access for scalar memory access.
+`-mno-strict-align`: The compiler allows misaligned access for scalar memory access.
+
+NOTE: The compiler may generate misaligned access if the program violates the alignment assumption.
+
 ## TODO
 
-* `-mdiv`, `-mno-div`, `-mfdiv`, `-mno-fdiv`, `-msave-restore`, 
-  `-mno-save-restore`, `-mstrict-align`, `-mno-strict-align`, 
-  `-mexplicit-relocs`, `-mno-explicit-relocs`
+* `-mdiv`, `-mno-div`, `-mfdiv`, `-mno-fdiv`, `-msave-restore`,
+  `-mno-save-restore`, `-mexplicit-relocs`, `-mno-explicit-relocs`
 
 ## Appendix: Exposing a vendor-specific extension across the toolchain