Add a brief README file for blazecli

Add a first version of a README that explains the basics of the blazecli
program.

Signed-off-by: Daniel Müller <[email protected]>

cli/README.md

@@ -0,0 +1,60 @@
+[![pipeline](https://github.com/libbpf/blazesym/actions/workflows/test.yml/badge.svg?branch=main)](https://github.com/libbpf/blazesym/actions/workflows/test.yml)
+[![rustc](https://img.shields.io/badge/rustc-1.63+-blue.svg)](https://blog.rust-lang.org/2022/08/11/Rust-1.63.0.html)
+
+blazecli
+========
+
+**blazecli** is a command line interface for the
+[**blazesym**][blazesym] library. It aims to closely mirror the
+structure of the library in its command and sub-command structure.
+
+
+Usage
+-----
+As mentioned above, the program's sub-command aim to mirror the
+library's public API structure. Hence, to symbolize an address in an ELF
+file -- which **blazesym** allows via the
+[`symbolize::Symbolizer`][blazesym-sym] type in conjunction with the
+[`Elf` source][blazesym-elf-src] -- is possible via the `symbolize elf`
+sub-command:
+
+```sh
+# Just an example to illustrate symbolization on live data.
+$ readelf --syms /lib64/libc.so.6 --wide | grep readdir64_r
+>   2253: 00000000000caee0   228 FUNC    WEAK   DEFAULT   12 readdir64_r@@GLIBC_2.2.5
+
+$ blazecli symbolize elf --path /lib64/libc.so.6 00000000000caee0
+> 0xcaee0: readdir_r@0xcaee0+0 :0
+```
+
+To run the program from within a checkout (without any kind of
+installation), you would use:
+```sh
+$ cargo run -p blazecli -- symbolize elf --path /lib64/libc.so.6 00000000000caee0
+```
+
+Similarly, to symbolize an address inside a process the `symbolize
+process` sub-command can be used. Please refer to the program's help
+text for additional details.
+
+
+### Shell Completion
+**blazecli** comes with shell completion support (for various shells). A
+completion script can be generated via the `shell-complete` utility
+program and then only needs to be sourced to make the current shell
+provide context-sensitive tab completion support. E.g.,
+```bash
+$ cargo run --bin=shell-complete --features="clap_complete" -- bash > blazecli.bash
+$ source blazecli.bash
+```
+
+The generated completion script can be installed system-wide and sourced
+through initialization files, such as `~/.bashrc`.
+
+Completion scripts for other shells work in a similar manner. Please
+refer to the help text (`--help`) of the `shell-complete` program for
+the list of supported shells.
+
+[blazesym]: https://crates.io/crates/blazesym
+[blazesym-sym]: https://docs.rs/blazesym/0.2.0-alpha.3/blazesym/symbolize/struct.Symbolizer.html
+[blazesym-elf-src]: https://docs.rs/blazesym/0.2.0-alpha.3/blazesym/symbolize/enum.Source.html#variant.Elf