Add bash marker to make README more readable

[jancionear]

This PR adds a bash marker to the examples sections in the README. With a bash marker the comments have a different color from the code, which makes it easier to distinguish between them.

This is more readable:

# or if the executable is already running, you can provide the PID via `-p` (or `--pid`) flag:
flamegraph [-o my_flamegraph.svg] --pid 1337

# NOTE: By default, perf tries to compute which functions are
# inlined at every stack frame for every sample. This can take
# a very long time (see https://github.com/flamegraph-rs/flamegraph/issues/74).
# If you don't want this, you can pass --no-inline to flamegraph:
flamegraph --no-inline [-o my_flamegraph.svg] /path/to/my/binary --my-arg 5

Than this:

# or if the executable is already running, you can provide the PID via `-p` (or `--pid`) flag:
flamegraph [-o my_flamegraph.svg] --pid 1337

# NOTE: By default, perf tries to compute which functions are
# inlined at every stack frame for every sample. This can take
# a very long time (see https://github.com/flamegraph-rs/flamegraph/issues/74).
# If you don't want this, you can pass --no-inline to flamegraph:
flamegraph --no-inline [-o my_flamegraph.svg] /path/to/my/binary --my-arg 5

[djc]

Thanks!