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

@@ -398,11 +398,26 @@ 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`
+Indicates that the compiler should not assume that unaligned scalar and
+unaligned vector memory references are handled by the system.
+
+`-mstrict-align`: The compiler disallows misaligned memory access.
+`-mno-strict-align`: The compiler allows misaligned memory access.
+
+NOTE: Non-strict also known as unaligned access or misaligned access
+NOTE: The compiler may generate misaligned access if the program violates the
+      alignment assumption.
+NOTE: The scope of this option isn't cover inline assembly.
+
 ## 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